If you’re publishing independently, you will deal with two file formats more than any others: PDF and EPUB. They solve fundamentally different problems, and confusing them — or using the wrong one in the wrong context — leads to rejected uploads, broken layouts, and frustrated readers.

This guide covers what each format does, where each one is required, and how they interact with the major publishing platforms.

PDF is for print. EPUB is for screens.

That’s the one-sentence version. Here’s why.

A PDF (Portable Document Format) is a fixed-layout document. Every element — every letter, every margin, every page break — is locked in place. When a printer receives your PDF, it reproduces exactly what you see on screen. This is why print-on-demand services like KDP and IngramSpark require PDF interiors: the file must specify the precise physical dimensions of every page.

An EPUB (Electronic Publication) is a reflowable document. The text adapts to the reader’s screen, font preferences, and text size settings. An EPUB doesn’t have “pages” in the PDF sense — it has chapters and sections that flow continuously, and the reading device decides where to break them. This is what Kindle apps, Apple Books, Kobo readers, and every other ebook platform expects.

The distinction matters because the constraints are completely different. A print PDF must match an exact trim size (say, 5.5” x 8.5”), embed all fonts, use the correct color space, and respect precise margin minimums for binding. An EPUB must be semantically structured, include proper metadata, and produce clean, readable text across hundreds of different screen sizes and reading apps.

They’re not interchangeable, and you almost certainly need both. Tools like Cambric export both formats from a single manuscript — one source, two outputs — so you don’t manage separate files for print and ebook.

What makes a good print PDF

A print-ready PDF is defined by physical constraints. Paper has a fixed size. Binding consumes part of the inside margin. Ink behaves differently in CMYK than on an RGB screen. The requirements:

  • Page dimensions match your trim size exactly. If you selected 5.5” x 8.5” on KDP, your PDF pages must be 5.5” x 8.5” — not letter size, not A4, not close enough.
  • All fonts are embedded. The print facility doesn’t have your fonts installed. If a font isn’t embedded, it gets substituted, and your typography falls apart.
  • Color space is correct. Black-and-white interiors should use grayscale. Color interiors need CMYK or sRGB depending on the platform.
  • Margins account for binding. The inside margin (gutter) must be wide enough that text doesn’t disappear into the spine. This minimum increases with page count.
  • No DRM or password protection. The printer needs to read the file. Encrypted PDFs get rejected.
  • Even page count. Physical books are printed on sheets, and sheets have two sides.

For a detailed walkthrough of print PDF requirements, see our guide on how to format a book for KDP. If you’re distributing through IngramSpark, their PDF specifications are stricter in some areas — our IngramSpark formatting guide covers the differences.

What makes a good EPUB

An EPUB file is actually a ZIP archive containing HTML files, a CSS stylesheet, metadata, and a table of contents. When you “write an EPUB,” you’re really producing a small, self-contained website packaged into a single file.

The key characteristics of a well-built EPUB:

  • Reflowable text. The reader controls font choice, font size, line spacing, and margins. Your EPUB must not fight this. Hardcoded font sizes, absolute positioning, and fixed dimensions break the reading experience.
  • Semantic structure. Chapters are separate HTML documents within the archive. Headings use proper heading tags. Emphasis uses <em>, not italic styling hacks. Screen readers and reading apps depend on this structure.
  • Metadata. Title, author, language, publisher, ISBN, cover image — all declared in the EPUB’s OPF file. Stores use this metadata for their catalogs, and readers see it in their libraries.
  • Table of contents. Both a machine-readable navigation document (for the reading app’s built-in TOC) and optionally a human-readable TOC page within the book content.
  • Embedded cover image. Every store requires a cover. In an EPUB, it’s embedded as part of the package, typically as a JPEG or PNG.
  • Clean CSS. Minimal, relative styling that suggests defaults without overriding the reader’s preferences. Heavy-handed CSS is the hallmark of a poorly converted EPUB.

EPUB 2 vs EPUB 3: what changed and why it matters

EPUB 2 was released in 2007 and served the ebook world for years. EPUB 3, finalized in 2011 and updated since, is now the standard. The differences matter more than you might think.

What EPUB 3 added:

  • HTML5 and CSS3. EPUB 2 used XHTML 1.1 and CSS 2. EPUB 3 uses modern web standards, which means better typography, more layout options, and support for web fonts.
  • Accessibility. EPUB 3 supports ARIA roles, semantic markup, and the EPUB Accessibility specification. This isn’t optional anymore — the European Accessibility Act requires accessible ebooks, and stores are beginning to enforce it.
  • Audio and video. EPUB 3 supports embedded media, enabling read-along books and multimedia educational content.
  • JavaScript. Limited scripting support for interactive content (quizzes, interactive diagrams).
  • Better navigation. The NCX table of contents from EPUB 2 was replaced with a proper HTML5 nav document, which is more flexible and more accessible.
  • MathML. Native support for mathematical notation, important for academic and technical publishing.

Why this matters for indie authors: If you’re publishing prose fiction or narrative non-fiction, the practical difference between EPUB 2 and EPUB 3 is mostly about accessibility and future-proofing. But some stores now require or strongly prefer EPUB 3. Apple Books, in particular, expects EPUB 3 and uses its features for better rendering. Producing EPUB 3 from the start avoids compatibility problems down the road.

Which stores accept what

This is where indie authors get tripped up. Each platform has its own requirements, and they’re not all the same.

Amazon KDP (Kindle): KDP accepts EPUB, DOCX, or KPF (Kindle Package Format) for ebook uploads. Internally, Amazon converts everything to their proprietary format (KFX for modern Kindles, MOBI/AZW for older devices). You never deliver a Kindle-native file directly — Amazon’s conversion pipeline handles it. This means the quality of your source EPUB matters enormously: a clean, well-structured EPUB converts well; a messy one produces a messy Kindle book.

Apple Books: Apple expects EPUB 3 specifically. They support advanced EPUB 3 features including fixed layout, embedded fonts, and multimedia. If you submit an EPUB 2 file, it may work, but Apple recommends EPUB 3 and their tooling is optimized for it.

Kobo: Kobo accepts both EPUB 2 and EPUB 3, reflowable and fixed-layout. Their reading apps handle EPUB 3 features well, including embedded fonts and advanced CSS.

Barnes & Noble (Nook Press): B&N accepts EPUB files, both EPUB 2 and EPUB 3, though EPUB 3 is recommended.

Draft2Digital, PublishDrive, and other aggregators: Most aggregators accept EPUB and distribute to multiple stores. They recommend EPUB 3, and some perform their own validation before forwarding to retailers.

The pattern is clear: produce a clean EPUB 3 file and it will work everywhere. EPUB 2 still functions on most platforms, but there’s no advantage to using the older spec. For a complete walkthrough of producing a quality ebook file, see our ebook formatting guide.

Fixed-layout vs reflowable EPUB

Most authors need reflowable EPUBs, but fixed-layout EPUBs exist for a reason.

Reflowable EPUB is what you think of when you think “ebook.” Text flows and adapts to the screen. The reader can change fonts, resize text, and adjust margins. This is correct for novels, memoirs, narrative non-fiction, and any book where the content is primarily text.

Fixed-layout EPUB works more like a PDF — each page has a set size and elements are positioned absolutely. This is appropriate for:

  • Children’s picture books where text is placed at specific locations relative to illustrations
  • Cookbooks with complex page layouts mixing photos, ingredient lists, and instructions
  • Comics and graphic novels where panels must maintain their spatial relationships
  • Art books and photography books where layout is integral to the content
  • Textbooks with complex figures where text wraps around diagrams in specific ways

If your book is primarily text, use reflowable. Full stop. Fixed-layout EPUBs don’t allow the reader to adjust font size or reflow text, which is a poor experience on small screens and breaks accessibility features. Some stores won’t accept fixed-layout files at all for text-heavy content.

Common mistakes

Submitting a PDF as your ebook file. This is one of the most common formatting mistakes in self-publishing. Some authors create a print PDF and try to upload it as an ebook. A few platforms will accept a PDF and attempt to convert it, but the results are almost always terrible. PDFs have no semantic structure — headings are just big text, chapters are just page breaks, and the entire concept of reflowable text doesn’t exist. Your ebook will have weird line breaks mid-sentence, no working table of contents, and text that’s either microscopic or enormous depending on the device.

Submitting a reflowable EPUB when you need fixed layout. If your children’s picture book has text overlaid on illustrations at specific positions, a reflowable EPUB will separate the text from the images and reflow it independently. The result is unreadable. Know which format your content requires before you start.

Ignoring metadata. An EPUB with missing or incorrect metadata — wrong language code, no author name, missing ISBN — may be accepted by a store but will display poorly in reader libraries and store catalogs. Metadata is not optional.

Over-styling the EPUB. Forcing specific fonts, fixed font sizes, and aggressive CSS overrides is tempting if you want your ebook to look like your print book. Resist this. Readers choose their own fonts and sizes for a reason. An EPUB that fights the reader’s preferences is an EPUB that gets returned for a refund.

Not testing on actual devices. Your EPUB looks perfect in Sigil or Calibre. It may look completely different on a Kindle Paperwhite, an iPad, or a Kobo Libra. Test on real devices or use the official preview tools (Kindle Previewer, Apple Books on macOS).

Do you need both formats?

Almost certainly, yes.

If you’re publishing a print edition through KDP or IngramSpark, you need a print-ready PDF. If you’re selling an ebook through any store — and there’s rarely a reason not to — you need an EPUB. These are separate files with separate requirements, and neither can substitute for the other.

Some authors start with ebook only and add print later, or vice versa. That’s fine. But the goal should be both, because each format serves a different reader. If you’re starting with ebook, our guide on how to format an ebook covers EPUB best practices in depth. If you need to convert an existing Word manuscript, see our Word to EPUB conversion guide. Leaving one format on the table means leaving readers and revenue on the table.

The challenge is that maintaining two separate workflows — one for print layout, one for ebook — doubles your formatting work. Every time you fix a typo, update your back matter, or change your chapter styling, you’re doing it twice. This is the problem that modern formatting tools are designed to solve. Cambric exports both a print-ready PDF and an EPUB 3 from the same project — one manuscript, one set of styling decisions, two output formats that stay in sync every time you re-export.

Before you export either format, run through our formatting checklist to catch common issues that cause rejected uploads or broken layouts.

One project, two formats

The practical solution is to work from a single source of truth. Your manuscript, front matter, chapter structure, and styling decisions live in one place, and your tool exports the appropriate format for each target.

Cambric works this way. You set up your book once and export a print-ready PDF and a clean EPUB 3 from the same project. Change a chapter title, fix a typo, update your Also By page, and both formats reflect the change on the next export. No parallel workflows, no version drift between your print and ebook files.

Whether you use Cambric or another tool, the principle holds: your format question shouldn’t be “PDF or EPUB” — it should be “how do I produce both without doing everything twice.”