EPUB vs PDF vs MOBI: Which to Use in 2026
Last updated September 2026.
When you're ready to publish your ebook, the first technical decision isn't about platforms or pricing — it's about format. EPUB, PDF, and MOBI are the three formats you'll encounter most often, and they behave very differently depending on where and how they're read.
Choosing the wrong format means readers get a poor experience, platforms reject your file, or your formatting breaks on certain devices. This guide explains what each format actually does, where it works well, where it fails, and exactly which one to use for each publishing scenario.
EPUB: The Industry Standard
EPUB is the format that every major ebook platform except Amazon uses as its primary format. Apple Books, Kobo, Google Play Books, Barnes & Noble, Smashwords, Draft2Digital, and IngramSpark all use EPUB. It's the ISO-standard ebook format and has been since 2007.
EPUB is a reflowable format. Text wraps to fit whatever screen size the reader is using — increase the font size and paragraphs reflow, switch from phone to tablet and the layout adjusts automatically. The reading experience adapts to the device, not the other way around.
Technically, an EPUB is a ZIP archive containing XHTML content files, CSS stylesheets, images, and XML metadata files (OPF for the manifest, NCX or nav for navigation). This structure is why EPUB errors happen — editing the wrong file, breaking the manifest, or creating malformed XHTML causes validation failures on strict platforms.
EPUB 3.0 is the current version of the standard. It supports HTML5, CSS3, embedded fonts, SVG, MathML, audio, video, and enhanced accessibility features. EPUB 2.0 still works on most platforms but is the older version with fewer capabilities and stricter constraints.
Use EPUB when: You're publishing anywhere other than Amazon, or when you're publishing wide across multiple platforms simultaneously. EPUB is also the right choice for the cleanest reading experience on e-readers and mobile devices.
Before uploading your EPUB anywhere, run it through the EPUB Validator to catch structural errors. Different platforms have different tolerance levels — what KDP accepts silently, Apple Books will reject with a terse error email.
MOBI: Amazon's Legacy Format (Discontinued for Publishing)
MOBI is Amazon's legacy ebook format, derived from an even older format called PalmDOC that predates the Kindle itself. Older Kindle devices — first and second generation e-ink Kindles from 2007–2010 — used MOBI natively. If you've ever seen a .mobi file in your downloads folder, it was almost certainly meant for a Kindle.
Amazon has been phasing MOBI out for years. KDP Direct Publishing stopped accepting MOBI file uploads in 2022. The current Kindle publishing format is KFX (Kindle Format 10), which Amazon generates internally from your EPUB submission. When you upload an EPUB to KDP, KDP converts it to KFX before delivering it to Kindle devices — you never deal with KFX directly.
MOBI files can still be sideloaded to Kindle devices via USB, and some older personal ebook libraries still contain .mobi files. But for publishing purposes in 2026, MOBI is a dead format. Don't create it for new projects.
Use MOBI when: You have a specific reason to sideload content to a personal Kindle device. For commercial publishing on any platform, do not use MOBI — submit EPUB and let the platforms handle conversion to their internal formats.
PDF: Fixed Layout for Print-Faithful Documents
PDF (Portable Document Format) is not a reflowable ebook format — it's a fixed-layout document format. Every element on every page is positioned at precise coordinates. Text doesn't reflow when font size changes. The layout doesn't adapt to screen size. A PDF of a book designed for 6x9 inch pages will render at 6x9 inches whether you're reading on a 5-inch phone or a 13-inch tablet.
This makes PDF excellent for documents where layout precision matters more than device adaptability: textbooks with complex figures, cookbooks with recipes and measurements in specific positions, technical manuals with diagrams, children's picture books where text and image placement is part of the design, and print-to-digital conversions where you want the ebook to look exactly like the print edition.
For standard prose — novels, memoirs, business books, narrative non-fiction — PDF is a poor choice. Reading a PDF novel on a phone means zooming in to read, then scrolling horizontally to reach the end of each line. The experience is significantly worse than EPUB, and readers will notice.
Platform support for PDF ebook distribution is limited. KDP accepts PDF for print book interior formatting (the physical book layout), not for ebook distribution to Kindle devices. Draft2Digital does not accept PDF for digital distribution. Kobo doesn't accept PDF. Google Play Books accepts PDF but renders it with limited quality. Apple Books accepts PDF but doesn't promote it.
Use PDF when: You're submitting a print book interior to KDP or IngramSpark for physical printing, or when you're publishing a heavily designed book (illustrated, technical, cookbook) where precise layout control matters more than device adaptability. For all prose books intended for reading on e-readers or phones, use EPUB.
Format Comparison at a Glance
Quick reference for format differences and platform requirements:
| Feature | EPUB | MOBI | |
|---|---|---|---|
| Reflowable text | Yes | No | Yes |
| Adapts to screen size | Yes | No | Yes |
| Open standard | Yes (ISO) | Yes (ISO) | No (Amazon) |
| KDP ebook upload | Yes (recommended) | No | No (discontinued 2022) |
| Apple Books | Yes (strict) | Limited | No |
| Kobo Writing Life | Yes | No | No |
| Google Play Books | Yes | Not recommended | No |
| Barnes & Noble Press | Yes | No | No |
| IngramSpark ebook | Yes | No | No |
| Print interiors (KDP, IngramSpark) | No | Yes (required) | No |
| Draft2Digital / Smashwords | Yes | No | No |
| Still actively published | Yes | Yes | No |
Note: These format requirements apply to ebook interior files. For cover image dimensions by platform — minimum pixel sizes, aspect ratios, and file size limits — see the book cover size guide.
Why KDP Accepts EPUBs That Other Platforms Reject
This is the most confusing part of publishing wide. You submit the same EPUB file to KDP and Apple Books. KDP publishes it. Apple Books sends a rejection email.
The reason: KDP converts your EPUB before publishing it. During that conversion, Amazon's systems silently fix or ignore many structural errors — invalid XHTML, ghost spacing, missing metadata fields. The resulting KFX file that reaches Kindle devices is cleaned up even if your EPUB was imperfect.
Apple Books doesn't do this conversion step. It delivers your EPUB directly to Apple devices. So every HTML error, every OPF problem, and every CSS conflict that KDP silently fixed becomes a rendering problem or a rejection when Apple Books processes the same file.
This means you can't use KDP acceptance as a proxy for EPUB quality. Run every EPUB through the EPUB Validator before uploading anywhere — it checks the same structural rules that strict platforms use, not the forgiving rules KDP uses.
Converting Between Formats
If you have a manuscript and need an EPUB, the Full Manuscript Mode converts your .docx or .txt directly to valid EPUB 3.0 in one step — with chapter detection, clean HTML output, proper OPF metadata, and a correctly structured navigation document.
Avoid converting from PDF to EPUB when possible. PDF-to-EPUB conversion produces consistently poor results because the fixed-layout structure of PDF doesn't map cleanly to reflowable EPUB. You typically get garbled text, broken paragraph structure, lost formatting, and missing images. If you only have a PDF, go back to the original manuscript source if at all possible.
Converting from MOBI to EPUB is possible using Calibre, but the output quality depends heavily on how the MOBI was originally created. MOBI files from personal sideloading typically convert adequately. MOBI files downloaded from retail platforms have DRM that must be removed before conversion — which may violate the platform's terms of service depending on your jurisdiction.
Pro Tips for Format Selection
- Build one EPUB, use it everywhere. A properly validated EPUB 3.0 works across all major ebook platforms. Don't maintain separate files per platform — one clean file with good metadata is all you need for wide distribution.
- Never use KDP acceptance as a quality signal. KDP's forgiveness means it accepts files that will fail on Apple Books, Kobo, and Google Play. Always validate independently before submitting to any platform. For a full list of reasons why platforms reject ebook files — cover issues, metadata problems, structural errors — see the complete guide to book rejection reasons.
- For illustrated books, consider fixed-layout EPUB. EPUB 3.0 supports fixed-layout mode for books where page layout is critical. This gives you more control than reflowable EPUB without the PDF compatibility problems. Use the EPUB Validator to check fixed-layout compliance before submitting.
Frequently Asked Questions
Does Amazon KDP still accept MOBI files?
No. KDP stopped accepting MOBI uploads in 2022. Submit EPUB to KDP — they convert it to their internal Kindle format (KFX) automatically. If you have older MOBI files for books you want to update, re-upload from your original EPUB or manuscript source, not from the MOBI file.
Can I use the same EPUB file for every platform?
Yes, with one caveat. A well-formed EPUB 3.0 file works across all major platforms. The caveat is that different platforms validate at different strictness levels — an EPUB that passes KDP's lenient checking may fail Apple Books' stricter validation. Run your EPUB through an independent validator before submitting to any platform. A file that passes a thorough validator will pass every platform's checks.
What's the difference between EPUB 2.0 and EPUB 3.0?
EPUB 3.0 is the current standard and supports HTML5, CSS3, MathML, embedded audio and video, SVG, and enhanced accessibility features including WCAG compliance. EPUB 2.0 is the older version, still widely supported but with fewer capabilities and stricter HTML constraints. If you're creating a new EPUB, use EPUB 3.0. Apple Books and Kobo are both optimized for EPUB 3.0, and some EPUB 3.0 features (enhanced TOC, accessibility metadata) only work in 3.0 format.
Is PDF acceptable for ebook readers?
Technically yes, practically no — for prose books. PDF works well for books where layout precision matters more than device adaptability: illustrated books, cookbooks, technical manuals, children's picture books. For novels and standard non-fiction, PDF gives readers a worse experience than EPUB on phone and e-reader screens. The fixed layout doesn't adapt to the reading device, making it uncomfortable to read on anything smaller than a tablet.
How do I know if my EPUB is high enough quality for wide distribution?
Run it through the BookKraft AI EPUB Validator. It checks the full EPUB specification — structure, HTML validity, OPF manifest, TOC, image references, CSS compliance, and accessibility markers. A file that passes this validator is ready for KDP, Apple Books, Kobo, IngramSpark, and every other major ebook platform. Zero errors in the validator means zero platform rejections from technical issues.