Top 3 eBook Formats for Authors in 2026: EPUB, Kindle & PDF

Last updated: September 2026 — rewritten for how eBook formats work today, now that MOBI has been retired.

For most authors in 2026, the answer is simple: you need an EPUB file for Apple Books, Kobo, Google Play, and most other stores, and a Kindle-ready file for Amazon — and a PDF only if you are publishing in print or selling downloads directly. The old MOBI format, which many guides still recommend, is no longer accepted by Amazon KDP.

This guide explains each eBook format in plain language — what it is, where it is used, and which ones you actually need for your book.

eBook Formats at a Glance

1. EPUB: The Universal eBook Format

EPUB is the open standard for eBooks. It is maintained by the World Wide Web Consortium (W3C) — the same organisation behind the standards of the web — and the current version is EPUB 3. Under the hood, an EPUB is a packaged set of web files: the text in HTML, the styling in CSS, plus your images, fonts, and a table of contents.

Because it is an open standard, EPUB is what almost every eBook store outside Amazon expects: Apple Books, Kobo, Google Play Books, Barnes & Noble, and aggregators such as Draft2Digital. Amazon KDP also accepts EPUB uploads.

Reflowable vs. Fixed Layout EPUB

• Reflowable EPUB — the text adapts to the screen and the reader’s chosen font size. Right for novels and most non-fiction.
• Fixed layout EPUB — every page keeps its exact design, like a printed page. Right for picture books, cookbooks, and comics. See our Fixed Layout ePub service.

Check It with EPUBCheck

Stores validate EPUB files with EPUBCheck, the W3C’s official validator. A file with errors can be rejected at upload, so every EPUB should pass it cleanly before you publish. Every file from our ePub conversion service is validated with it.

2. Kindle Formats: KPF and What Amazon Accepts

For Amazon, you don’t need a special “Kindle format” of your own making. KDP accepts three main formats for eBook uploads: DOCX, EPUB, and KPF (Kindle Package Format). Amazon then converts your upload into its own delivery formats for Kindle devices and apps — you never need to create those yourself.

• KPF is produced by Amazon’s free tools, Kindle Create and Kindle Previewer. It is a finished, packaged file, so edits are made in the source and the KPF is rebuilt.
• EPUB is often the best upload for books with images, tables, or footnotes — one well-built EPUB can serve both Amazon and every other store.
• DOCX works for simple, text-only books with clean Word styles.

Always preview your book in Kindle Previewer before publishing. For a file built and checked by hand, see our Kindle Conversion service — and for the full upload process, read how to upload a book on Amazon Kindle in 2026.

3. PDF: For Print, Not for E-Readers

A PDF keeps every page exactly as designed, which is why it is the standard format for print: KDP Print and IngramSpark both take your paperback interior as a print-ready PDF. See our KDP Print Paperback formatting.

That same fixed page is what makes PDF a poor eBook. On a phone or e-reader, the text can’t reflow to fit the screen, so readers have to zoom in and scroll sideways on every line. PDFs work well for workbooks, printable guides, and downloads sold directly from your own website — but for eBook stores, use EPUB.

What Happened to MOBI?

MOBI was Amazon’s original Kindle format, and older guides — including many still ranking in search — tell authors to upload a .mobi file. That advice is out of date: KDP no longer accepts MOBI files. If you have an old MOBI edition, the text and styling can be rebuilt as an EPUB, which will work on Amazon and every other store.

Which eBook Formats Do You Need?

Converting Your Book Between Formats

Most books start as a Word document, an InDesign file, or a PDF. Automated converters can turn these into EPUB or Kindle files, but they often produce bloated code, broken tables of contents, and files that fail validation. Starting from a well-structured manuscript makes the biggest difference — our free Word templates and Kindle Formatting Checklist help — and for a clean, validated result, hand-coded conversion starts at $30.

New to the terminology? Our eBook glossary explains EPUB, KPF, reflowable, fixed layout, and more.

Frequently Asked Questions

What is the best eBook format?

EPUB. It is the open standard, accepted by Apple Books, Kobo, Google Play, Barnes & Noble, and Amazon KDP, and it adapts to any screen size.

Does Amazon Kindle use EPUB?

Amazon KDP accepts EPUB uploads and converts them into its own delivery formats for Kindle devices and apps. You can publish on Amazon with a well-built EPUB.

Is MOBI still used?

No longer for publishing. KDP does not accept MOBI files, so use EPUB, KPF, or DOCX instead.

Is PDF a good eBook format?

Not for e-readers or phones, because the text can’t reflow to fit the screen. PDF is the right format for print interiors and for downloads you sell directly.

Do I need separate files for Kindle and other stores?

Often one well-built EPUB can serve every store, including Amazon. Many authors still order a dedicated Kindle file alongside the EPUB so each is optimised for its platform — which is what our Kindle + ePub Bundle provides.