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Glossary

What is KF8 (AZW3)?

Updated:

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.

How EpubCC handles it: it does not write KF8, AZW3 or MOBI files. It writes EPUB, and Amazon's Send to Kindle service, which lists EPUB among its supported formats (help page read on 2026-11-04), converts it for the device. MOBI is no longer in that list, so EPUB is also the format Amazon itself now expects for personal documents.

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FAQ

What is KF8 (AZW3)?

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.