Complete Ebook File Formats Glossary: EPUB, MOBI, KPF for KDP Publishers

AZW (Amazon Word) - Amazon's proprietary ebook format used before MOBI adoption. Legacy format still found on older Kindle devices but no longer accepted for new KDP uploads. Why it matters: Understanding AZW helps troubleshoot compatibility issues with readers who have older Kindle libraries.

AZW3 - Enhanced version of AZW format supporting improved typography and layout features. Replaced by KPF in 2022 but still used for some enhanced ebooks. Why it matters: AZW3 files offer better formatting control than standard MOBI, crucial for complex layouts.

EPUB (Electronic Publication) - Industry standard ebook format based on HTML, CSS, and XML. Supported by virtually all ebook readers except Amazon Kindle devices. File extension .epub with typical sizes ranging 1-5MB for text-heavy books. Why it matters: EPUB is mandatory for wide distribution beyond Amazon, reaching 40% more potential readers across platforms like Apple Books, Kobo, and Google Play.

KPF (Kindle Package Format) - Amazon's newest ebook format replacing MOBI for KDP uploads since August 2022. Supports enhanced features like improved typography, better image handling, and advanced layout options. Why it matters: KPF enables features that can increase reader engagement by 15-20% according to Amazon's internal data, potentially boosting your book's algorithm ranking.

MOBI (Mobipocket) - Amazon's legacy ebook format, still supported but no longer the default for new uploads. Files typically 20-30% larger than EPUB equivalents due to compression differences. Why it matters: Understanding MOBI is essential for managing backlist titles uploaded before 2022 and troubleshooting conversion issues.

DRM (Digital Rights Management) - Copy protection technology applied to ebook files to prevent unauthorized sharing. Amazon applies DRM to all KDP titles by default, while some platforms offer DRM-free options. Why it matters: DRM affects how readers can share or transfer your books between devices, potentially impacting word-of-mouth marketing.

Enhanced Typesetting - Advanced text formatting features available in KPF and AZW3 formats, including improved hyphenation, kerning, and spacing. Not supported in standard MOBI files. Why it matters: Enhanced typesetting can improve reading experience and reduce negative reviews related to formatting issues.

Fixed Layout - Ebook format option that maintains exact page positioning, essential for children's books, cookbooks, and graphic novels. Supported in KPF, AZW3, and EPUB3. Why it matters: Fixed layout prevents text reflow issues that can make image-heavy books unreadable on different screen sizes.

Reflowable Text - Standard ebook format allowing text to adjust automatically to different screen sizes and font preferences. Default setting for most fiction and non-fiction titles. Why it matters: Reflowable text ensures accessibility across all device types, crucial for maximizing your potential readership.

Vector Graphics Support - Ability to include scalable images that maintain quality across different screen resolutions. Supported in KPF and EPUB3 but limited in older MOBI files. Why it matters: Vector graphics ensure your book covers and interior images look crisp on high-resolution devices like iPad Pro and newer Kindles.

CSS (Cascading Style Sheets) - Code language used to control ebook formatting and appearance. Essential for custom styling in EPUB and KPF formats. Limited support in legacy MOBI files. Why it matters: CSS knowledge allows precise control over your book's appearance, potentially increasing reader satisfaction and reducing returns.

File Size Limits - Maximum allowable ebook file sizes vary by platform: Amazon KDP allows up to 650MB, while most other platforms cap at 20-50MB. Why it matters: Exceeding file size limits can prevent publication or increase delivery costs, directly affecting your royalties.

HTML5 - Latest version of markup language used in modern ebook formats like EPUB3 and KPF. Provides enhanced multimedia and interactive capabilities. Why it matters: HTML5 support enables advanced features like embedded audio, video, and interactive elements that can differentiate your book.

Metadata - Embedded information within ebook files including title, author, publication date, and keywords. Stored differently across formats but essential for discoverability. Why it matters: Proper metadata ensures your book appears in relevant searches and recommendation algorithms across all platforms.

UTF-8 Encoding - Character encoding standard supporting international characters and symbols. Required for proper display of non-English text in all modern ebook formats. Why it matters: Incorrect encoding can cause character display issues, particularly problematic for books containing accented characters or non-Latin alphabets.

Calibre - Free, open-source ebook management software capable of converting between virtually all ebook formats. Supports batch conversion and metadata editing. Why it matters: Calibre eliminates the need for expensive conversion software and allows indie authors to manage multiple format requirements efficiently.

DPI (Dots Per Inch) - Image resolution measurement crucial for ebook graphics and covers. Amazon recommends 300 DPI for print-quality images, 72-150 DPI for screen-optimized ebooks. Why it matters: Incorrect DPI settings can result in blurry covers or oversized files that slow download times.

Kindle Previewer - Amazon's free tool for testing how ebooks will display across different Kindle devices and apps. Supports KPF, MOBI, and converted EPUB files. Why it matters: Previewer testing can catch formatting issues before publication, preventing negative reviews and returns.

EPUB3 - Latest version of EPUB format supporting multimedia, interactivity, and enhanced accessibility features. Backward compatible with EPUB2 readers. Why it matters: EPUB3 capabilities can justify premium pricing for enhanced non-fiction titles with interactive elements.

Sideloading - Process of manually transferring ebook files to devices outside official store channels. Commonly used for EPUB files on Kindle devices via email conversion. Why it matters: Understanding sideloading helps you assist readers who want to access your books across multiple platforms.

Apple Books - Requires EPUB format with specific metadata requirements and enhanced accessibility features for optimal store placement. Supports advanced typography and multimedia. Why it matters: Apple Books represents approximately 15% of the US ebook market, making EPUB mastery essential for wide distribution success.

Draft2Digital - Aggregator service that converts your manuscript to multiple formats for distribution across various platforms. Accepts Word documents and converts to platform-specific requirements. Why it matters: D2D simplifies wide distribution by handling format conversion automatically, though you sacrifice some formatting control.

Google Play Books - Accepts EPUB and PDF formats, with EPUB strongly preferred for reflowable content. Requires specific metadata schema for optimal discoverability. Why it matters: Google Play Books reaches Android users who might not find your book through other channels, representing untapped revenue potential.

IngramSpark - Print-on-demand service that also distributes ebooks in EPUB format to libraries and bookstores worldwide. Requires professional-grade formatting standards. Why it matters: IngramSpark's library network can provide steady passive income through institutional sales that individual platforms can't access.

Kobo - Canadian-based platform accepting EPUB format with enhanced support for international markets and currencies. Strong presence in Canada, Japan, and parts of Europe. Why it matters: Kobo's international focus makes it valuable for authors targeting non-US markets, where Amazon's dominance is less pronounced.

EPUB vs EPUB3 - EPUB refers to the general format family, while EPUB3 is the specific latest version with multimedia support. Many platforms still use EPUB2 for basic text books. Practical difference: EPUB3 enables interactive features but isn't always necessary for simple fiction titles.

MOBI vs AZW - MOBI is the format name, while AZW is Amazon's container for MOBI files with added DRM. Functionally similar for basic reading but AZW includes Amazon's proprietary features. Practical difference: AZW files only work on Amazon devices, while MOBI can theoretically work on other readers.

KPF vs KFX - KPF is the source format authors upload to KDP, while KFX is the delivery format Amazon creates for newer Kindle devices. Authors never directly create KFX files. Practical difference: KFX provides better reading experience but is automatically generated from your KPF upload.

Fixed Layout vs Reflowable - Fixed layout maintains exact positioning like a PDF, while reflowable text adjusts to screen size and user preferences. Choice affects which devices display your book properly. Practical difference: Fixed layout required for image-heavy books but limits accessibility options.

DRM-Free vs DRM-Protected - DRM-free ebooks can be freely transferred between devices and backed up, while DRM-protected files are locked to specific accounts and platforms. Practical difference: DRM-free books may see more sharing but also more piracy, while DRM-protected books ensure platform lock-in but limit reader flexibility.