# What is KF8 (AZW3)?

Source: https://epublab.com/glossary/kf8-azw3/ (updated 2026-11-03)

KF8 (Kindle Format 8) is Amazon's e-book format based on HTML5 and CSS, introduced in 2011; files in this format usually have the .azw3 extension. It replaced the older MOBI format on Kindle devices.

## Why it matters when you convert a PDF to EPUB

You do not need to produce KF8 or AZW3 yourself to read a converted PDF on a Kindle: Send to Kindle takes an EPUB and converts it. Producing EPUB keeps one file that works on Kindle, Kobo and every other reader.