7 Ebook Formats Explained: EPUB, MOBI, PDF, AZW3 & More

1. EPUB (Electronic Publication)

File extension: .epub

Type: Reflowable

Created by: International Digital Publishing Forum (now W3C)

EPUB is the most widely supported ebook format in the world. It’s an open standard, meaning anyone can create EPUB files without paying licensing fees. Under the hood, an EPUB is a ZIP archive containing XHTML files, CSS stylesheets, images, and metadata.

Key features:

• Reflowable text that adapts to any screen size
• Supports embedded fonts, images, audio, and video (EPUB 3)
• Adjustable font size, family, and line spacing
• Chapter navigation and table of contents
• DRM support (Adobe DRM, Readium LCP)

Supported by: Apple Books, Google Play Books, Kobo, Nook, most third-party reading apps. Not natively supported on Kindle (but Amazon added EPUB support in 2022).

Best for: Novels, non-fiction books, textbooks, and any content where comfortable reading matters more than exact layout.

2. PDF (Portable Document Format)

File extension: .pdf

Type: Fixed-layout

Created by: Adobe Systems

PDF is the universal document format. Every element has a fixed position on the page, so a PDF looks identical on every device and printer. While it’s not technically an “ebook format,” PDFs are widely used for ebooks, especially academic papers, textbooks, and technical manuals.

Key features:

• Pixel-perfect layout on every device
• Supports annotations, forms, digital signatures
• Embedded fonts and vectors
• Print-ready output
• Universal support (opens on virtually any device)

Best for: Printing, academic papers, legal documents, image-heavy publications, and anything where exact layout matters.

3. MOBI (Mobipocket)

File extension: .mobi

Type: Reflowable

Created by: Mobipocket SA (acquired by Amazon)

MOBI was the original Kindle format before Amazon developed its own proprietary formats. It’s based on the Open eBook standard and was the primary format for early Kindle devices. Amazon officially stopped accepting MOBI uploads in 2024, but millions of MOBI files still exist in personal ebook libraries.

Key features:

• Reflowable text with basic formatting
• Image support
• DRM support (Amazon’s DRM)
• Works on older Kindle devices and apps

Best for: Legacy Kindle content. For new ebooks, EPUB or KF8/AZW3 is preferred.

4. AZW3 / KF8 (Kindle Format 8)

File extension: .azw3

Type: Reflowable (with fixed-layout option)

Created by: Amazon

AZW3, also known as Kindle Format 8 (KF8), is Amazon’s modern ebook format. It replaced MOBI as the standard Kindle format and supports HTML5 and CSS3, enabling much richer formatting than the older MOBI format. AZW3 files can include custom fonts, SVG graphics, and complex layouts.

Key features:

• HTML5/CSS3 support for rich formatting
• Custom embedded fonts
• Fixed-layout support for comics and children’s books
• Amazon DRM

Best for: Kindle publishing and reading on Kindle devices/apps.

5. AZW (Amazon Word)

File extension: .azw

Type: Reflowable

Created by: Amazon

AZW is Amazon’s original proprietary format, essentially a DRM-protected MOBI file. When you purchase a book from the Kindle store, it downloads in AZW format. The format itself is nearly identical to MOBI but includes Amazon’s DRM wrapper.

Best for: Purchased Kindle books (used automatically by Amazon).

6. FB2 (FictionBook)

File extension: .fb2

Type: Reflowable (XML-based)

Created by: Dmitry Gribov

FB2 is an XML-based ebook format popular in Russia and Eastern Europe. It stores the book’s structure (chapters, paragraphs, emphasis) as XML elements, making it very clean and easy to convert to other formats. While less common in Western markets, FB2 has a dedicated following and many apps support it.

Best for: Russian/Eastern European ebook libraries and users who prefer a clean, structured format.

7. PRC (Palm Resource Compiler)

File extension: .prc

Type: Reflowable

Created by: Palm, Inc.

PRC is a legacy format from the Palm PDA era. It’s structurally similar to MOBI and can be read by Kindle apps. While essentially obsolete for new content, many older ebook libraries contain PRC files that users may need to convert.

Best for: Legacy ebook collections from the Palm/Mobipocket era.