Main Ebook Formats
- EPUB 3: open W3C standard. The most universal ebook format.
- MOBI: legacy Mobipocket format. Deprecated by Amazon since August 2022.
- AZW3 (KF8): Amazon's modern Kindle format. Kindle and Kindle apps only.
- PDF: not a native ebook format but widely used.
EPUB: The Open Standard
EPUB compatibility:
- ✅ Kobo, Apple Books, Google Play Books, Adobe Digital Editions
- ✅ Moon+ Reader, Aldiko (Android)
- ❌ Kindle (Amazon accepts EPUB on KDP since 2022 but converts it to AZW3)
MOBI: Deprecated
Amazon stopped accepting MOBI on KDP in August 2022. Older Kindles still support it but the format lacks modern features.
AZW3: Modern Kindle Format
Full HTML5 and CSS3 support. Kindle Paperwhite, Kindle Oasis, Kindle apps on iOS/Android. Not compatible with non-Amazon readers. Amazon auto-generates AZW3 when you upload EPUB.
Format Comparison
| Format | Kindle | Kobo | Apple | Open |
|---|---|---|---|---|
| EPUB 3 | ❌ (indirect) | ✅ | ✅ | ✅ |
| MOBI | ✅ (legacy) | ❌ | ❌ | Partial |
| AZW3 | ✅ | ❌ | ❌ | ❌ |
Convert with Calibre
ebook-convert book.epub book.mobi
ebook-convert book.epub book.azw3
ebook-convert book.mobi book.epub --output-profile kindle_pw3
Convert with Pandoc
pandoc book.docx -o book.epub --metadata title="Title"
pandoc chapters.md -o book.epub --epub-cover-image=cover.jpg
Publishing on KDP
Amazon KDP accepts EPUB (recommended), DOCX, and HTML. MOBI is no longer accepted since August 2022.
Workflow: write in Word → upload EPUB → Amazon generates AZW3 → preview with Kindle Previewer.
Which Format to Choose?
| Situation | Format |
|---|---|
| Publishing on Kindle | EPUB (KDP converts it) |
| Publishing on Kobo, Apple, Google Play | EPUB 3 |
| Multi-store distribution | EPUB 3 |
| Fixed-layout technical document |
Conclusion
EPUB 3 is the standard format for modern publishing. Amazon accepts EPUB on KDP and converts it to AZW3. The old MOBI is deprecated. For multi-store compatibility, EPUB 3 guarantees maximum reach.
Advanced Use Cases
Legal and business workflow: signed contracts are distributed in PDF/A (PDF Archival) which guarantees the document renders identically in 50 years — all fonts embedded, no JavaScript, no dynamic content. Electronic signature (PAdES, advanced eSignatures) is integrated in PDF and validates cryptographically. Academic publishing: theses and papers use LaTeX → PDF for precise mathematical formulas; journals require specific format (Word with styles, LaTeX with journal class, or both). Converting between LaTeX, DOCX and PDF preserving semantic structure (citations, references, equations) requires specialized tools like Pandoc. E-books: Amazon KDP requires MOBI (legacy) or KFX (modern) format generated from EPUB; Apple Books accepts EPUB natively; Kobo, PocketBook and Nook prefer EPUB; Google Play Books accepts PDF and EPUB. Converting DOCX manuscript to EPUB requires attention to semantic markup (hierarchical headings, lists, blockquotes) so reflowable layout works well. Translation workflows: professional translators prefer XLIFF as intermediate format — maintains segmentation, translation memory matches, and context info that is lost in plain text export.
Best Practices and Professional Tips
Style preservation: when converting between editable formats (DOCX↔ODT↔RTF), always use defined styles instead of direct formatting — Heading 1/2/3 vs "16pt Bold". This guarantees outline preservation and conversion maintains hierarchical structure. Font embedding: for cross-platform distribution (PDF), embed all non-standard fonts — without embedding, readers automatically substitute with available fonts which can break layout. PDF/A for archival: for legal, regulatory or permanent archive documents, export as PDF/A-1b (basic) or PDF/A-2u (Unicode + JPEG2000) — doesn't allow dynamic content, guarantees self-contained rendering. Revision history: PDF, DOCX and ODT support tracked changes and comments — when converting, decide if you want to preserve them (DOCX→DOCX or DOCX→ODT) or flatten them (DOCX→PDF typically accepts only the final state). Accessibility: PDF documents for public distribution should comply with PDF/UA — heading structure, alt text on images, defined reading order for screen readers.
Compatibility and Technical Considerations
KaijuConverter uses LibreOffice 7.6 headless as the main engine with Pandoc 3.x as fallback for complex markup conversions. We support more than 60 document formats (PDF, DOCX, DOC, ODT, RTF, TXT, HTML, MD, EPUB, MOBI, AZW3, FB2, LaTeX, RST and more). Format fidelity: we preserve fonts (with substitution fallback if original font is not on system), sizes, colors, complete paragraphs with indentation and line spacing, nested lists, tables with cell merging and complex borders, embedded images with anchor positioning, headers/footers with dynamic fields (page number, date, document title), footnotes and endnotes. PDF conversion: we guarantee PDF/A-conforming output when required, with correct font embedding and ICC profile embedding for absolute color fidelity. Limitations: documents with macros (DOCX with VBA) don't execute macros during conversion — only static content is preserved. Scanned PDFs (image without OCR) are not editable — they need previous OCR (Tesseract, ABBYY) to extract text. Privacy: TLS 1.3, isolated Docker containers, deletion after 2 hours. Performance: typical 20-page document takes 3-8 seconds; large documents with many images may require 15-30 seconds.
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