What is the Kindle KFX format? How can you read Kindle KFX books? Which devices support Kindle KFX? And how do you convert KFX to PDF? If you’re looking for the answers, just keep reading.
Although the Kindle KFX format was released in 2015, it significantly impacted Amazon Kindle book readers in early 2017 when the Kindle for PC/MAC automatically updated to version 1.19. Since then, nearly all Kindle books downloaded via the Kindle desktop application have been in KFX format.
Subsequently, users discovered that Kindle books in this format could only be opened with Kindle devices or Kindle-related applications. So, what exactly is the Kindle KFX format? This is what I aim to share with you. I will address the concerns you may have regarding Kindle KFX. As the old saying goes, "Know thyself, ever-victorious." Let's uncover the mysterious veil of the Kindle KFX format.
1. What is a Kindle KFX file?
Kindle KFX format, known as kindle 10, is the successor to the azw3 format and released with the Kindle Paperwhite 3. This new format was featured a new enhanced typesetting engine and new Bookerly font. The Amazon Kindle books with enhanced typesetting enabled feature can be downloaded in Kindle KFX format.
To further dig, the Amazon uses a new image format called JXR which is higher compressed than JPG.
For downloaded content of the Kindle KFX format, you will not see a single book under the My Kindle Content folder, but a subfolder included the whole content of the book.
For the Kindle KFX eBook downloaded via Kindle for PC/MAC, it contains the content like the following picture.
For the Kindle KFX downloaded via Kindle device, it will be a little bit different.
The encrypted eBook content is stored directly in Document folder of my Kindle voyage with the title as: Telling Lies (A Sam Mason Mystery Book 1)_B06XQ655PC.kfx.
At the Document folder, you can also find the .sdr folder with the same name as the book title: Telling Lies (A Sam Mason Mystery Book 1)_B06XQ655PC.sdr. All userful contents of this book is stored at a subfolder named assets. Below are the contents in assets folder.
If you miss any file, the book cannot be considered as an integrated book.
2. What is Kindle kfx-zip file?
When I upload my newly downloaded Kindle books via kindle for pc to calibre, I found them display as kfx-zip file. There's no way for me to open such files. what's the difference between kfx and kfx-zip?
The Kindle KFX-ZIP file is not the actual ebook downloaded to your computer via Kindle for PC or Mac. Only Calibre users will encounter KFX-ZIP files when they fail to remove Kindle KFX DRM with Calibre DeDRM. Additionally, they must have the Calibre input and output plugins properly installed. We can consider the presence of KFX-ZIP files as an indication of the failure to remove Kindle KFX DRM using Calibre.
Now we can distinguish between KFX and KFX-ZIP, right? The KFX file is the Kindle book downloaded via Kindle for PC/Mac, while the KFX-ZIP is the file generated by Calibre when DRM removal fails.
3. Why Can't I send to Kindle a kfx? Which Devices Support Kindle KFX Format
Although Kindle KFX has been released for many years, not all Kindle devices or Kindle reader apps support this format because it is use special rendering techique. The following table shows the Kindle kfx format supported devices and apps.
| Kindle devices with firmware<5.8 | Kindle devices with firmware=5.8 | Kindle for PC v1.19 and above | Kindle for PC v1.21 and later | Kindle for iOS v6.03 and later | Kindle for Android v7.2 and later | Kindle Previewer v2.94 | |
|---|---|---|---|---|---|---|---|
| kfx | × | v(with extension .kfx) | v | v | × | v(with extension .kfx) | × |
v: KFX format can be read on the device or with the app.
×: KFX format cannot be read on the device or with the app.
Does Kindle Cloud Reader Support KFX?
No, the Kindle Cloud Reader does not directly support KFX files, which are Amazon's proprietary e-book format.
Why Can't I send to Kindle a kfx? Send-to-kindle delivering KFX format to Kindle Devices
The "Send to Kindle" tool converts non-Kindle formats into Kindle's native format (KFX) and synchronize them with your library. However, it cannot process formats that are already proprietary Kindle formats, such as KFX. That's why you cannot send to kindle a kfx file.
Instead, utilize "Send to Kindle" with your non-DRM EPUB files. This feature will seamlessly convert EPUB files to KFX and transmit them to your library via cloud sync, while preserving metadata, typically completing the process in just a minute. It is worth noting that only Kindle ereaders that support KFX format are getting personal documents delivered in KFX now (at least the Kindle Paperwhite 3 and newer).
4. How to Read Kindle KFX Files on Any Device?
Although the KFX format has many new features, but it seems it is not welcome by many readers as it has much more limitations than before. That's why there are limited reading app that supports kindle kfx format. By default, KFX is locked inside Amazon’s ecosystem.
How to read Kindle kfx on Any device?
If you want to open Kindle KFX on non-Kindle devices or apps (like Calibre, Moon+ Reader, Kobo, etc.), you’ll need to convert the KFX files first. Here is the simple stepes: To read KFX on any reader, you'll need to remove DRM first and convert kfx to EPUB/PDF, and finally transfer kindle to your device or app. That's what we will discuss further in the following part.
5. How to Remove Kindle kfx DRM
It is universal known that Kindle kfx has been encrypted with Kindle kfx DRM, so if we want to back up our Kindle books, or read it on other reader apps or eReader, we have to remove Kindle KFX DRM at first.
Here meet our Epubor Ultimate—the first tool on the market can decrypt and convert Kindle KFX to epub/mobi/pdf/azw3. The decrypted and converted file will keep the original quality.
Step 1. Download and Install Epubor Ultimate.
Epubor Ultimate works on both Windows and Mac system smoothly.
Step 2. Run Epubor Ultimate to remove Kindle kfx DRM.
When you run Epubor Ultimate, the books you downloaded via Kindle for PC/MAC, or Kindle device will be side loading at the left column on the interface. Just drag the books from the left column and drop them to the right column. All books will be decrypted automatically.
You can find the decrypted books by clicking the "Decrypted" at the end of each book or clicking the folder icon on right bottom.
6. How to convert kfx to pdf? Can I convert Kindle kfx file with Calibre?
Recently, I’ve received many emails about the issue of reading DRM-free Kindle KFX books in Calibre. Many readers have complained that even after removing DRM from their Kindle KFX eBooks, they still cannot open or read them in Calibre. While Calibre supports most popular eBook formats on the market, such as AZW, MOBI, EPUB, AZW3, PDF, CBR, and more, Kindle KFX is unfortunately not included in that list.
We regret to inform you that Calibre does not support reading Kindle KFX files directly. If you want to open KFX books in Calibre, you need to convert KFX to EPUB, MOBI, PDF, or AZW3 using Epubor Ultimate.
Once you’ve removed the DRM from your KFX books, simply select “PDF” as the output format and click the “Convert to PDF” button to start the process. Within seconds, your Kindle KFX files will be converted to PDF with Epubor Ultimate. With this all-in-one tool, you can easily remove DRM and convert KFX to PDF while preserving the original quality. Why not give it a try?
Some Calibre users may wonder if they can convert the Kindle kfx file with Calibre? Yes, but you need to install Dedrm plugin to Calibre first and then convert kindle kfx to PDF/epub with Calibre.
Now you can read Kindle KFX with Calibre. These are all things about Kindle KFX format I collected for you guys. If you still have concerns about the Kindle kfx, please leave them at the comments.
Frequently Asked Questions on kindle kfx format
Q: If I fail to remove Kindle kfx DRM, what should I do?
A: You can follow this troubleshooting guide Kindle KFX DRM Removal Failed and Solutions to resolve the issue.
Q: Can I remove Kindle kfx DRM from books downloaded via Android device?
A: It might not be possible to remove kfx DRM from books obtained from Kindle for android apps. But you can download kindle books via Android emulator and then remove drm with the Epubor Kindle Converter.
Q: Can I use Calibre to convert Kindle KFX format eBooks now? How to?
A: With the latest De-DRM plugin installed, you can convert KFX to pdf/epub/mobi/txt with Calibre. Please read How to convert Kindle kfx to epub/pdf/mobi with calibre to learn how to convert kfx to pdf with Calibre converter.
Iris Yan Marketing Architect at Epubor since 2017, drives the brand’s product design, advertising, and all-channel strategy.
Cheers
John