Reference
Ebook formats explained: EPUB, AZW, PDF and DRM
Short answer
EPUB is the open standard that opens nearly everywhere except Kindle apps. Kindle uses AZW3 and KFX, which open only in Amazon's apps. PDF is a fixed page image and reads badly on phones. DRM, not format, is what actually locks a book: a DRM-free EPUB is portable forever, and a DRM-protected one is not.
Last checked 2026-08-01 — steps, prices, and links are desk-reviewed, not verified at a live checkout. Tell us if something moved and we will date the fix.
What is EPUB?
An open, reflowable format maintained by the W3C. Text adapts to screen size and font settings, which is why it reads well on a phone. Kobo, Apple Books, and almost every third-party reader open it natively.
Amazon accepts EPUB files through Send to Kindle but converts them on delivery, so the file in your Kindle library is no longer an EPUB.
What about Kindle formats?
AZW3 and the newer KFX are Amazon's own formats. They support advanced typography and are readable only in Amazon's apps and devices, with no supported export path for purchases.
Why DRM matters more than format
DRM is the licence enforcement wrapped around a file. A DRM-free EPUB or MP3 works in any app, backs up to your own storage, and survives any company. A DRM-protected file works only where the seller allows, for as long as the seller exists.
This is why our lock-in tables list DRM and export path separately from format: the format tells you what opens it, DRM tells you whether you may.
Which format should you buy?
DRM-free EPUB wherever it is offered, then EPUB with DRM, then Kindle formats last. In audio, DRM-free MP3 or M4B from Libro.fm sits at the top of the same ladder.
| Format | Opens in | Reflows | Typically DRM'd |
|---|---|---|---|
| EPUB | Kobo, Apple Books, most readers | Yes | Sometimes |
| AZW3 / KFX | Kindle apps and devices only | Yes | Almost always |
| Everything | No | Rarely | |
| MP3 / M4B | Any audio player | n/a | No, when bought DRM-free |
Q & A
Questions readers actually ask
- Can I convert a Kindle book to EPUB?
- Not legally where DRM is present, since stripping it breaks the licence terms in most jurisdictions. DRM-free files convert freely with tools like Calibre.
- Is EPUB better than PDF for reading?
- On phones and e-readers, yes. EPUB reflows to your screen and font size; PDF holds a fixed page layout designed for paper.
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