An Overall Introduction to Kindle KFX Files

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KFX is the latest Amazon Kindle format which was released with Kindle Paperwhite 3. A KFX file refers to Kindle Format 10 eBook, successor to the AZW3 (KF8) format. Amazon rolled out KFX format in 2015 to take advantage of Bookerly font, and they used KFX for the standard book since then. In this article, I’ll illustrate what KFX format is, what the new features of KFX files are, how to open and read KFX files, and how to remove KFX DRM and convert KFX to PDF/EPUB/MOBI/AZW3/TXT.

1. New features of KFX format
2. How to open and read a DRMed KFX file?
3. Explanation of KFX content: files composed of a KFX eBook
4. How to remove KFX DRM and convert convert KFX to PDF/EPUB/MOBI/AZW3/TXT?

New features of KFX format

Many of you may wonder what features the KFX format possesses. The new format is designed to give you the optimal reading experience with Kindle books. Amazon also adds its DRM scheme for digital rights protection and anti-piracy to KFX format.

In the past many Kindle book have been criticized by the typesetting problems such as the awkward spacing between words and lack of hyphens. The new KFX format improves text justification and automatically adjusts margins and layout to better fit the screen with large font sizes. It improves word spacing, hyphenation, and character placement. Other additions include soft hyphens, page flip, kerning, drop caps, the new image format with higher compression called JXR, and the new artistry Bookerly font. Bookerly, the Kindle-exclusive font, emulates the style of the best fonts in modern print books while providing great readability on digital screens of all sizes.

KFX-features bookerly-font

Not all Kindle books delivered by Amazon use the new KFX format. Then how to identify whether a Kindle title uses the new KFX format? Well, you can check on the book’s description page at Amazon and see a new label that shows if the Enhanced Typesetting is enabled. You can take a look at the highlighted part in the screenshot as shown below:


If the book titles are labeled as Enhanced Typesetting enabled in Amazon product description, and you want to upgrade your purchased eBooks from older formats to KFX, you just need to delete these books from your Kindle device and re-download them again. This way you’ll get your purchased eBooks in the new Amazon KFX format.

How to open and read a DRMed KFX file?

All books delivered by Amazon in KFX format have DRM encryption. Therefore, you can only open and read a DRMed KFX file on Kindle related Kindle devices or apps.

Kindle Devices Windows Mac iOS Android
Kindle eInk Readers and newer Fire Tablets with firmware higher than 5.8 (eg: Paperwhite 3, Voyage, Oasis, Oasis 2, Kindle Fire HD) Kindle for PC v1.19 and above,
Kindle Previewer 3
Kindle for Mac v1.19 and above,
Kindle Previewer 3
Kindle for iOS v6.03 and above (file extension must be .azw) Kindle for Android v7.2 and above (file extension must be .kfx)

If you want to read KFX files with Calibre, you need to strip the DRM from the KFX files and convert their files to Calibre compatible formats. See more information in this article: How to Open/Read Kindle KFX ebook with Calibre

Explanation of the KFX Content

A KFX file is not a sole eBook content file, instead, it contains the Amazon encrypted eBook content, DRM voucher, and metadata describing the book such as the author, title, categories, key words, and number of pages.

A complete KFX eBook downloaded via Kindle for PC/Mac higher than version 1.19 are made up of various files, see the screenshot below:


The files that make up a KFX eBook downloaded via Kindle eInk device differ from those comprised of a KFX book downloaded via Kindle for PC/Mac. Under Kindle/Documents, you’ll see a book title with .kfx extension and a folder named after the book title with .sdr extension:



Within the sdr folder, there’s a subfolder called asset, see the contents in the asset folder shown in the screenshot below:


As you can see that books in KFX format are usually composed of multiple KFX container files. The entire set of KFX files that make up the book is required for successful DRM removal and format conversion.

How to remove KFX DRM and convert KFX to PDF/EPUB/MOBI/AZW3/TXT?

Now we know that all KFX books are encrypted with DRM protection by Amazon. If you want to archive your KFX books, share your purchases to your friends, or read them on any portal device or app freely, you have to remove DRM from the KFX books and convert them to other formats if needed.

Epubor Ultimate is the only tool out there to remove DRM from KFX files directly without installing any plug-in or downgrading the version of Kindle for PC/Mac. It’s easy to operate and handle your KFX files efficiently.


To ensure the successful DRM removal and format conversion, please don’t relocate the path that stores the KFX files. You must keep the entire KFX files that make up the eBook intact. Any file or subfolder is missing will lead to failure of DRM removal or format conversion.

KFX books downloaded from Kindle for PC/Mac v1.19 or later are saved in .azw extension. While the KFX books downloaded from Kindle eInk Readers are saved in .kfx extention.

If the KFX books are stored in your Kindle e-ink Reader, please connect your Kindle device to your computer via USB cable. Make sure the books are downloaded on your Kindle device rather than saving in Cloud.

If you don’t have a Kindle e-ink Reader, please install Kindle for PC/Mac of version higher than 1.19 on your computer. Sign in the Kindle reading app with your Amazon account, and you’ll see your Kindle Library. Make sure the KFX books you’d like to remove DRM are downloaded to your local computer.

Step 1. Install Epubor Ultimate

Download Epubor Ultimate for free


Step 2. Run Epubor Ultimate

Once you launch Epubor Ultimate, it will detect and load your Kindle books from your Kindle eInk Reader and Kindle desktop app automatically.

Click on “eReader or “Kindle” tab, and you’ll see all your Kindle books are listed in the left side column. You can also drag and drop the KFX books to the main interface of the program. The KFX books are decrypted automatically when they’re loaded to the program.



You can see a checkmark and "Decrypted" next to the KFX books you've removed DRM from. Click on "Decrypted", the decrypted file output folder will prompt automatically.


On the bottom part, you can choose the output conversion format, click “Convert to XXX” button, and the program starts to decrypt the books and convert the formats simultaneously. Once the conversion is done, you can see "succeeded" next to the book title.


Heads up: Please ensure the KFX books are purchased via your own Amazon account and downloaded via Kindle e-ink device or Kindle for PC/MAC installed on your computer. The books must be associated with your Amazon account. Loaned books or books obtained from other sources cannot be supported by the program.

You can download the software for free by clicking the links below. The trial version of Epubor Ultimate handles DRM removal and format conversion of 20% contents of your original eBooks. If you want to get 100% contents of eBooks decrypted and convert their formats losslessly, you need to upgrade Epubor Ultimate to the paid version.

Download Epubor Ultimate for free



Sisi is a newbie who joined Epubor in November 2017. She's a bookworm her whole life and has taken great interest in eBooks recently. She learns professional knowledge about ebooks in Epubor and loves to share her know-how to all the ebook lovers!

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