E-book Formats Explained — EPUB, MOBI, AZW3, PDF, and More
July 13, 2026
When I bought my first Kindle back in 2011, I assumed all e-books were the same. You download a file, you read it on your device, done. Then I tried to open a library book on it and hit the wall that every new e-reader owner eventually hits: format incompatibility.
E-books come in a bunch of different formats, and they're not all created equal. Some are open standards. Some are proprietary locks designed to keep you inside a specific ecosystem. Some are great for novels but terrible for comics. Some are basically just images stuffed into a folder and renamed.
Let's break them down so you know what you're actually dealing with.
Frequently Asked Questions
EPUB. It's the industry standard for everything except Kindle. Open, flexible, and widely supported.
Modern Kindles use AZW3 and KFX. Older ones used MOBI. Kindle now accepts EPUB via Send to Kindle with automatic conversion.
AZW3 is the newer format with better typography and formatting. MOBI is the older, simpler format. Both are Amazon proprietary.
They're image archives for comics. CBZ is ZIP-based, CBR is RAR-based. Both store full-resolution page scans for comic reading apps.
Yes, with the right tools. DRM-free books convert easily between formats. DRM-protected books are locked to their ecosystem.