A KFX file is an eBook that is created in the Amazon Kindle File Format 10 (KF10) for Kindle devices. A KFX file is an eBook created in the Kindle Format 10 (KF10), Amazon's successor to the. Tutorial explaining how to convert e-books in KFX format to other Kindle formats using Calibre with DeDRM and KFX Input plugins, including. Then click "Download" button to download the book to your computer. The KFX eBook file format. Most KFX files are categorized as Raster Image Files, which can be opened by numerous software packages.