EPUB vs PDF: Which Format Is Better for Reading on iPhone?

You found the book or document you want, and it comes as both an EPUB and a PDF. Which one do you actually grab? The short answer is that EPUB is almost always the better choice for reading a book on a phone, and PDF wins when the exact page layout is the content rather than the container. The longer answer depends on what you are reading, where it came from, whether you need to cite it, and how small your screen is.

This post breaks down the difference between EPUB and PDF in plain language, goes through the places the difference actually bites (typography, footnotes, equations, accessibility, file size, page numbers), explains what conversion between them costs you, and ends with a straight recommendation for each kind of reader. Neither format is simply better. They were built for different jobs, and most of the frustration people have with both comes from using one for the other's job.

The short version

What is an EPUB?

EPUB (.epub) is the standard, open format for ebooks, maintained by the W3C. Its current version, EPUB 3.3, became a W3C Recommendation in May 2023, which is the same standing given to the web's own specifications. Almost every ebook from a library, an open catalog, or a non-Kindle store comes as an EPUB.

Structurally, an EPUB is a ZIP archive containing XHTML files, CSS, images and a manifest. If that sounds like a small website in a box, that is exactly what it is, and it explains everything else about the format. The defining consequence is that EPUB is reflowable: the text is not tied to a fixed page. Change the font size and the words rewrap. Turn your phone sideways and the layout adjusts. Read on a 6-inch phone and then on an 11-inch iPad and the same book fills each screen properly instead of forcing you to pinch and pan.

Think of an EPUB as a stream of text and images plus instructions for how to display it, not a snapshot of finished pages. That is why it adapts to you, and it is also why two people reading the same EPUB may be on completely different page numbers.

What is a PDF?

PDF (.pdf) is a fixed-layout format, standardised as ISO 32000, with PDF 2.0 published in 2017 and revised in 2020. It captures a document exactly as it was designed, down to the position of every line, image and page break, and it carries the fonts it needs inside the file so nothing shifts on a machine that lacks them. Open the same PDF anywhere and it looks identical, which is precisely the point. A PDF of a tax form, a sheet of music, or a glossy art book preserves a layout that would fall apart if the text were allowed to reflow.

There is a second, quieter fact about PDFs that matters more than most comparisons admit. A PDF may or may not contain text at all. A file exported from Word or LaTeX contains real characters you can select and search. A file produced by a scanner contains photographs of paper and nothing else, so there is no text in it to select, search, highlight or read aloud until somebody runs OCR over it. Both are .pdf, and they behave completely differently. Try selecting a word: if nothing happens, you have a scan.

The trade-off with the fixed page is the obvious one. On a small screen you are either zoomed out reading tiny text or zoomed in and scrolling sideways to follow each line. PDFs do not adjust to your screen the way EPUBs do, because adjusting would break the layout they exist to protect.

Reflowable text versus a fixed page

This is the difference that produces every other difference, so it is worth being precise about.

An EPUB reflows. A paragraph that runs three lines on an iPad might run five on an iPhone, and that is fine, because the text simply fills whatever width it is given. The page is generated at the moment you look at it, from your font, your size and your margins.

A PDF does not reflow. A page laid out for A4 stays that shape forever. On a phone, your device has two options and neither is good: shrink the whole page to fit the width, which makes the text small, or show it at readable size, which means the page is wider than the screen and you pan sideways on every line. Apple Books demonstrates this most bluntly, because it offers no font size control for PDFs at all. There is no reflowable text there to resize, only a page image to zoom.

Why this hurts more on a phone than on a tablet

The comparison people should be making is between the physical page the document was designed for and the physical glass in their hand. An A4 or Letter page is roughly the size of a large tablet held in portrait, so a PDF page on an iPad in portrait is close to actual size and reads fine. The same page on a phone is being reduced to a fraction of its designed size, and everything on it, including type intended to be read at ten or eleven points on paper, shrinks with it.

That is why the honest advice for PDFs is device-shaped rather than app-shaped: read them on the biggest screen you have. Landscape helps, trimming the printed margins helps, and a two-page spread on an iPad in landscape turns the tablet into something close to an open book. On a phone, no setting fully rescues a dense A4 page.

The escape hatch, and its cost

A few apps reconstruct the text out of a PDF and pour it into a single adjustable column, usually called Reading Mode. PDF Expert does it, and Readdle notes it is an iPhone feature rather than an iPad one. Readdle's free Documents app has the same mode, and Foxit has had a reflow view on mobile for years. It is a genuine feature and it is worth knowing about.

It is also a reconstruction, not a translation. The app is guessing at reading order from the position of glyphs on the page, which works well on a single-column article and badly on a two-column journal paper with floating figures, sidebars and running headers. Complex tables and equations are exactly where the guess fails. Reading Mode is a good answer to "this text is too small"; it is not a way of turning a PDF into an EPUB.

Typography: what you control in each format

Because an EPUB is reflowable, nearly everything about its appearance is yours: the typeface, the size, the weight, line height, word and letter spacing, paragraph spacing, first-line indent, alignment, hyphenation, margins and colours. Publisher styles can be honoured or overridden. In justRead you can go further and import your own .ttf and .otf files, or a whole .zip of a font family, from inside the reader, which is the only route to reading everything in a face you actually like. Japanese vertical writing (tategaki) flows right to left as it should, and an iPad can run one column or two per orientation. The full range is laid out on the customization page.

A PDF locks all of it. The fonts, sizes, spacing and column widths are part of the page description, and a reader has no flexible text layer to rearrange. You can zoom, you can trim the printed margins to reclaim width, you can change the background behind the page, and you can switch between paginated and scrolling views. You cannot swap the typeface or change the point size, in justRead or in any reader that is not doing the Reading Mode reconstruction described above.

This cuts both ways, and the PDF side of it is real. A typographer who has set a book carefully, chosen a face for the text and balanced the margins, gets exactly that book delivered to every reader. An EPUB of the same book arrives in whatever the reader's app defaults to, which is frequently a system font at a size the designer would wince at. If the design of the book is part of the book, the PDF is the faithful copy.

Footnotes, tables, images and equations

This is where the abstract difference becomes concrete, and it is the section most format comparisons skip.

Footnotes. In a PDF, a footnote sits at the bottom of the page it belongs to, because pages are real things in that format. In an EPUB, there is no fixed page, so footnotes are links: tap the marker and a well-built EPUB 3 shows the note in a popup without losing your place, while a badly built one throws you to an endnotes file at the back and leaves you to find your way home. For heavily annotated academic work, this single behaviour is often the deciding factor, and it varies by publisher rather than by format.

Tables. A PDF renders a table exactly as designed. An EPUB has to fit a table into an unknown width, and a wide table on a phone either scrolls sideways in its own box, shrinks to illegibility, or breaks. Anything with more than three or four columns is usually more readable as a PDF.

Images and diagrams. Both formats embed images fine. The difference is placement. A PDF holds a figure next to the text that refers to it, because that relationship was fixed at layout time. An EPUB flows the figure into the stream, so on a small screen it can land a screen or two away from its caption's context. For a diagram-led manual, fixed placement genuinely wins.

Equations. A PDF renders mathematics as laid out, always correctly, but as static marks. EPUB 3 supports MathML, which means equations can scale with your font size and can be read by assistive technology as mathematics rather than as decoration. In practice, support depends on the reading app, and many EPUBs ship equations as images anyway, which reintroduces the scaling problem. For serious mathematical text, PDF remains the more reliable delivery, and that is unlikely to change soon.

Accessibility: screen readers, speech and large print

Accessibility is the area where the two formats differ most and where the difference is least understood.

An EPUB is structured HTML. Headings are marked as headings, lists as lists, the reading order is explicit, and the text is text. A screen reader knows what it is looking at, and large print costs nothing because the text simply reflows at whatever size you set. EPUB Accessibility 1.1 was published alongside EPUB 3.3, which gives publishers a testable standard to claim conformance against.

A PDF may be equally accessible or not accessible at all, and you cannot tell by looking. The mechanism is the tagged PDF, a separate structure tree that labels each piece of content as a heading, a paragraph, a list item, a table cell or a figure. The standard for this is PDF/UA, ISO 14289, and where a file is properly tagged the experience is good. Where it is not, the file is, as far as software is concerned, a set of glyphs positioned on a page. A screen reader has to guess what is a heading and what order to read things in, and it frequently guesses wrong, reading a two-column paper straight across both columns. A scanned PDF with no OCR layer is worse still: there is nothing there to read at all.

This has a direct practical consequence in reading apps, and it is a good illustration of the format difference rather than a limitation someone chose. justRead's Read Aloud speaks any EPUB that has no narration of its own, with the sentence being read highlighted, the current word underlined, and the page turning itself on the word being spoken. You can use an Apple voice in any of the app's seventeen languages, or download one of eight English neural voices that run on the device with no account and no signal, set the speed anywhere from 0.75x to 2x, add a sleep timer, and keep it playing in the background with Lock Screen controls. It works on EPUBs and not on PDFs, and the reason is the format: Read Aloud needs a clean, ordered stream of text to speak, which is what an EPUB is by construction and what a PDF only sometimes is.

Both formats benefit from the app-level accessibility work that sits outside the file: VoiceOver labels throughout the app, Dynamic Type, Line Focus to dim everything but the line you are on, and the ability to import OpenDyslexic or any other typeface you read better in. That last one applies to EPUBs only, for the same reason as everything else in this section.

File size, and why the two differ so much

An EPUB of a novel is small. Text compresses extremely well, the whole package is a ZIP archive, and what makes an EPUB large is images rather than words. A classic from Project Gutenberg is a trivial download even over a poor connection.

PDFs vary enormously depending on how they were made. A PDF exported from a word processor is text plus embedded font subsets, and is also small. A PDF exported from a design tool with high-resolution images is much larger. A scanned PDF is the extreme case: it stores a full-page image for every single page, so a scanned book dwarfs anything text-based, and it is the reason a few scanned volumes can occupy more space on your phone than a thousand ebooks.

Size matters more than it used to on a phone, not because storage is scarce but because it decides how a library behaves. Small files sync quickly, download on demand without a wait, and can be kept offline in bulk. A library of scanned PDFs syncs slowly and fills a device. If you are choosing what to keep locally on an iPhone, that is the pragmatic axis.

Page numbers, and why students should care

An EPUB has no inherent page numbers. Page count is generated from your font size and margins, so it changes when you change them, and it differs between your phone and your tablet. Percentage through the book is the stable measure, which is fine for reading and useless for citation. If your seminar is discussing page 214, and your ebook says you are 43 percent through, you have a problem.

There are two ways out. EPUB 3 lets a publisher embed invisible page-break markers that record where each printed page began, exposed through a page-list navigation element so a reader can map on-screen position back to the print edition. Where a publisher has done that work, an EPUB cites as well as a print copy. Many have not. The other way out is the PDF, where a page is a real, permanent thing and the number in the corner is the number everyone else is looking at.

This is the strongest single argument for PDF in academic work, and it is the reason course readers, journal articles and legal documents are distributed as PDFs and will continue to be. If you are going to quote it in something that gets marked, graded or filed, the PDF of the published version is the safer copy, whatever it costs you in comfort.

DRM and who actually owns the file

Neither format is inherently locked, and both can be.

An EPUB from Project Gutenberg, Standard Ebooks, a publisher's own store or an author's website is a plain file you own. An EPUB from a commercial store or a library loan may be wrapped in Adobe DRM, which arrives as an .acsm ticket rather than a book and requires an authorised app to open. Those are not readable in a general-purpose reader, and no amount of importing will change that.

A PDF can carry a password to open it, and can also carry permission flags intended to restrict printing or copying. The first is genuine encryption; the second is a request that software is expected to honour. justRead opens password-protected PDFs once you type the password. It does not remove DRM of any kind from either format, which is the correct behaviour and also the reason a library loan will not open in it.

The practical rule is simple: the format tells you nothing about whether you own the file. The source does.

Where each format comes from

Knowing the source usually tells you which format you will get:

• Ebooks from public libraries, Project Gutenberg, Standard Ebooks and most non-Kindle stores arrive as EPUB.
• Documents such as academic papers, manuals, contracts and reports are almost always PDF.
• Scanned material, like a photographed old book or a scanned chapter, is nearly always a PDF, because it is really a sequence of page images.
• Exports from a word processor can be either, but PDF is the common default when someone wants the file to look the same everywhere.
• Comics and manga are usually neither. They travel as CBZ or CBR archives, which are just ZIP or RAR files full of page images, and a PDF of a comic is generally a worse version of the same thing.

If you have a choice between an EPUB and a PDF of the same book, the EPUB is usually the cleaner reading copy. PDFs of books are often just print pages saved to a file, complete with wide print margins, running headers and a page number that wastes a line at the bottom of every screen.

Converting between them, and when it wrecks the layout

Converting is asymmetric, and understanding why saves a lot of wasted evenings.

EPUB to PDF works. You are going from a flexible description to a fixed one, which means the software only has to make decisions, not guesses. Calibre does it well. It is worth doing when you want to print something, or pin a specific layout for distribution.

PDF to EPUB usually does not. You are asking software to reconstruct meaning from position. Calibre's own manual is blunt about it: PDF documents are "one of the worst formats to convert from", because they are a fixed page size and text placement format, which makes it very hard to work out where one paragraph ends and another begins. Headers and footers become body text, hyphenation from justified print columns leaves broken words scattered through the file, two-column layouts interleave, and footnotes migrate into the middle of sentences. Calibre's newer PDF input engine detects and strips headers and footers automatically, which helps, and its output is still an approximation.

The rough guide to whether it is worth trying:

• Single-column, text-only, digitally produced PDF. Conversion often produces something readable. Worth a try.
• Two-column academic paper. Do not bother. Read it as a PDF on the largest screen you have, or find the publisher's HTML version.
• Anything with tables, figures or equations. Do not bother. You will lose exactly the parts you were converting for.
• A scan with no text layer. Conversion produces an empty file, because there is no text to convert. OCR it first, then reconsider.

The better move, whenever it is available, is not to convert at all but to find the book in the format you want. For anything out of copyright, an EPUB from Project Gutenberg or Standard Ebooks will be a better reading copy than any conversion of a scan.

When to choose EPUB

Pick EPUB when:

• You are reading a novel, a biography, or any book that is mostly running text.
• You read on a phone, where reflow and adjustable font size make the biggest difference.
• You want to control the font, size, spacing, margins and colours.
• Your eyes get tired and you need larger text or a warmer background at night.
• You want the book read aloud to you.
• You use a screen reader, or you need genuinely large print.
• You keep a large library and want files that sync quickly and stay small.

For the vast majority of book reading, EPUB is the format you want. If you are setting one up for the first time, our guide on how to read EPUB on iPhone and iPad walks through opening a file, importing a library and tuning the page so it is comfortable.

When to choose PDF

Pick PDF when:

• The exact layout is the point: forms, sheet music, technical diagrams, recipes with precise plating, or art and photography books.
• You need page numbers that match everyone else's, for citation or for a class.
• The document is a scan, so it has no real text layer to reflow anyway.
• Tables, figures and equations carry the argument.
• You need the file to look identical to how the author or publisher intended, with no risk of the layout shifting.
• It is the only format available, which is often the case for academic papers and official documents.

A PDF is the right call when you genuinely need the page preserved. Just be realistic about small screens: a dense PDF page is harder to read on a phone than on an iPad, where the larger display shows a full page at a comfortable size. If most of your PDF reading is on the larger screen, see our companion guide on how to read PDF on iPhone and iPad.

Which format for which reader

The lists above are the general case. Here is the same decision for specific people.

You read novels on a phone. EPUB, without hesitation. Reflow is the entire game at that screen size, and there is no argument on the other side.

You are a student with assigned readings. You will be handed PDFs and you do not get a vote. Read them on the largest screen you have, in landscape, with the margins trimmed, and highlight in an app whose highlights can leave the app. Keep the PDF as the citable copy even if you read a converted version for comfort.

You are a researcher who quotes what you read. Either format, but decide where your highlights live before you make a thousand of them. This is the trap in the category, and it is not hypothetical: Readwise's own documentation states that "Apple Books doesn't create 'real' highlights on PDFs according to the PDF spec, so you'll need to use a different app to get these highlights into Readwise." Highlights made in the wrong app are stranded there permanently.

You read art, photography, cookery or design books. PDF, or the publisher's fixed-layout EPUB if one exists. Reflowing a designed page destroys the thing you bought it for.

You read comics or manga. Neither. Use CBZ or CBR, which are built for the job and which justRead reads in the same library as everything else.

You need large print, or you use a screen reader. EPUB, and check for an accessibility claim if the publisher makes one. A PDF is a gamble unless you know it is tagged.

You would rather listen than look. EPUB. That is the format Read Aloud speaks.

You are keeping something for twenty years. PDF, and specifically PDF/A if you get the choice. That is ISO 19005, an archival profile of PDF that forbids the features which age badly, such as linked fonts and encryption, and requires everything needed to display the document to sit inside the file. It is the conservative bet for something you want to open unchanged in decades.

Reading both formats on iPhone and iPad

You do not have to pick one format for your whole library, and you do not need separate apps. justRead reads both EPUB and PDF, along with CBZ and CBR comics and your own audiobook files, so your novels, your papers and your documents live in the same place, in one library with one search box and one set of statistics.

The two formats behave differently inside the app, which matches how they behave everywhere:

• EPUB gets the full set of reading controls: system fonts or any typeface you import, font weight and size, line height, word and letter spacing, paragraph spacing, first-line indent, alignment, hyphenation and ligatures, separate margins for portrait and landscape, one or two columns on iPad, and custom text and background colours from named presets that can follow light and dark mode or the real sunrise and sunset where you are. Every one of these can be set for a single book, so a dense reference text and a relaxed novel keep their own look. Read Aloud works here.
• PDF keeps its page, and gets everything that does not require reflowing it: paginated or scrolling reading, vertical or horizontal scroll, page fit and spacing, a two-page spread with an offset first page on iPad, full-text search, password-protected files, and colour inversion so a white scanned page becomes genuinely dark at night rather than a bright rectangle inside a dark app. What a PDF does not get is typography control, text reflow and Read Aloud.

The important correction to a common assumption: highlighting works the same in EPUBs and PDFs. Six colours, one of which is a red underline, a full note editor on any highlight, a per-book list showing the text, colour, position, date and your note, and one browser across every highlight in every book. Those highlights export the same way from both formats too, as a PDF, as Markdown, or straight to Readwise with your own token. Bookmarks, reading progress and the reading position that catches up to the furthest page you reached on another device all work identically across the two formats as well.

A few other things are format-blind by design. Calibre Content Server sync brings PDFs across alongside your EPUBs, and pushes your progress and ratings back the other way, which is covered on the Calibre sync page. The library format filter lets you browse EPUB and PDF separately or exclude one with a double tap, and you can edit the title, author, series and tags on a PDF just as on an EPUB, which is what stops a shelf of coverless documents from becoming a wall of grey tiles. The ebook library page shows how that scales. Both formats feed the same statistics and streaks, and the 20-20-20 break timer runs in both readers.

What justRead does not do to a PDF is edit it: no Apple Pencil or freehand ink, no form filling, no page editing, and no Reading Mode reflow. If your main need is marking up documents with a Pencil or signing them, a dedicated PDF tool is the right answer and there is no shame in keeping two apps. The PDF book reader page sets out that line in detail, and our best apps for reading PDF books on iPhone and iPad roundup covers the rest of the field.

One honest note: justRead is an iPhone and iPad app. There is no Mac, Windows or Android version. If that is a dealbreaker, this is the place to know it before you start.

EPUB vs PDF FAQ

Is EPUB or PDF better for reading on iPhone?

EPUB is better for most books, because it reflows to your screen and lets you change the font, size, spacing and colours. PDF is better when you need to preserve an exact layout, cite fixed page numbers, or read a scan, an illustrated book or something equation-heavy. On a small phone screen, EPUB's reflow is a decisive comfort advantage for text-heavy reading.

Can I highlight a PDF, or is that EPUB only?

You can highlight a PDF, provided the file has a real text layer rather than being a scan. In justRead, highlighting works the same in PDFs as in EPUBs: six colours, notes on any highlight, and export to PDF, Markdown or Readwise from either format. The thing to check before you start is whether your app's PDF highlights can leave the app, because in some of them they cannot.

Can justRead read both EPUB and PDF?

Yes, in the same library, along with CBZ and CBR comics and your own audiobook files. EPUB gets the full typography and layout controls because it is reflowable, and it is the format Read Aloud speaks. PDF keeps its fixed page, and gets paginated and scrolling reading, vertical or horizontal scroll, a two-page spread on iPad, search, colour inversion, highlights, notes, bookmarks and progress tracking. There is no ink markup, form filling or page editing for either.

Can a PDF be read aloud?

Not in justRead. Read Aloud speaks EPUBs, because it needs a clean ordered stream of text and that is what an EPUB is by construction. A PDF may have a broken reading order or, if it is a scan, no text at all. Some dedicated text-to-speech apps will attempt a PDF; the quality depends entirely on whether the file was tagged properly when it was made.

Which format do most ebooks come in?

Most ebooks from public libraries, Project Gutenberg, Standard Ebooks and non-Kindle stores come as EPUB. PDF is more common for documents, academic papers, manuals, and scanned or heavily illustrated books. If you are downloading a regular book to read, you will usually find an EPUB.

Can I change the font in a PDF reader?

In most readers, no. A PDF bakes its fonts and layout into each page, so there is no flexible text to restyle. You can zoom, trim the printed margins and switch between paginated and scrolling views, but not swap the typeface. Apps offering a Reading Mode reconstruct the text into a single adjustable column, which works well on simple documents and poorly on complex ones. To freely change fonts, sizes and spacing, read the EPUB version of the same content.

Should I convert my PDFs to EPUB?

Usually not. Calibre's own manual calls PDF one of the worst formats to convert from, because working out where paragraphs begin and end from a fixed page layout is genuinely hard. A single-column text-only PDF sometimes converts acceptably. A two-column paper, anything with tables or equations, and any scan without OCR will not. Look for the book in EPUB form instead.

Why does a PDF look worse than an EPUB on my phone?

Because the PDF is a fixed page sized for print or a larger screen, so your phone shrinks the whole page to fit and the text shrinks with it. An EPUB rewraps the text to your screen width at whatever size you choose. This is why PDFs read better on an iPad than on a phone, and why EPUB is the friendlier format for small screens.

Which format is better for citing in an essay?

PDF, in almost every case. Its page numbers are fixed and match the printed edition, so a quotation you attribute to page 214 is on page 214 for your reader too. An EPUB's page count depends on your font size unless the publisher embedded print page markers, which many do not. Read for comfort in whichever format you like; cite from the PDF.

The practical takeaway

For everyday book reading, choose EPUB and let the text adapt to your eyes and your screen. Reach for PDF when the layout itself is the content, when you have to cite fixed pages, or when it is the only version that exists. Do not spend an evening converting between them unless the source is a simple single-column document; the conversion loses exactly the things that made you want the fixed layout in the first place.

If you keep both kinds of file, and most people do, an app that reads both saves you from juggling two libraries and two sets of highlights. That is what justRead is built for: EPUB reading with deep typography control and Read Aloud, PDF reading that treats a document as a book rather than a preview, the same highlights and progress across both, and one library on iPhone and iPad. You can see the full picture on the features overview.

For the next steps, see how to read EPUB on iPhone and iPad, how to read PDF on iPhone and iPad, the PDF book reader overview, the reading customization options, and our roundup of the best apps for reading PDF books on iPhone and iPad.