eBook Format Guide: EPUB, MOBI, PDF, and AZW3
Navigate the eBook format landscape. Understand reflowable vs fixed-layout formats, DRM implications, and how to choose the right format for publishing and personal reading.
Key Takeaways
- eBook formats split into two paradigms.
- EPUB is essentially a ZIP archive containing XHTML content, CSS styling, and metadata.
- Amazon Kindle uses proprietary formats (MOBI, AZW3/KF8).
- Use PDF only for content where exact layout matters — textbooks with complex diagrams, sheet music, manga, or technical manuals with precise page references.
Reflowable vs Fixed Layout
eBook formats split into two paradigms. Reflowable formats (EPUB, MOBI) adapt text to any screen size — the reader controls font size, margins, and line spacing. Fixed-layout formats (PDF) preserve exact page design but cannot adapt to different screens. Most prose books should use reflowable formats.
Format Comparison
| Format | Type | DRM | Ecosystem | Standard |
|---|---|---|---|---|
| EPUB 3 | Reflowable/Fixed | Optional | Open (Apple, Kobo, Google) | W3C |
| MOBI | Reflowable | Kindle DRM | Amazon Kindle (legacy) | Proprietary |
| AZW3 (KF8) | Reflowable | Kindle DRM | Amazon Kindle | Proprietary |
| Fixed layout | Optional | Universal | ISO |
EPUB: The Open Standard
EPUB is essentially a ZIP archive containing XHTML content, CSS styling, and metadata. EPUB 3 supports JavaScript, MathML, SVG, audio, and video. It is the standard format for Apple Books, Google Play Books, Kobo, and most independent bookstores.
The Amazon Ecosystem
Amazon Kindle uses proprietary formats (MOBI, AZW3/KF8). Amazon's Send to Kindle service now accepts EPUB files and converts them internally. For self-publishing on Amazon, upload EPUB — Amazon converts to their internal format automatically.
PDF for eBooks: When and Why
Use PDF only for content where exact layout matters — textbooks with complex diagrams, sheet music, manga, or technical manuals with precise page references. For everything else, EPUB provides a superior reading experience across devices.
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