If you like to buy audiobooks from iTunes store, you should know that the iTunes audiobooks are DRM protected and can't be played on android devices or any other Non-Apple devices. However, some useful 3rd party apps can help you out, like TunesKit AudioBook Converter.
TunesKit DRM Audiobook Converter for Windows Best audiobook DRM removal...
In this article, I want to share my experience of how to add my purchased iTunes audiobooks to Amazon Kindle Fire hd
Step 1. Download and Install TunesKit AudioBook Converter.
Windows version: http://www.tuneskit.com/download/AudiobookConverterForWin.exe
Mac version: http://www.tuneskit.com/download/AudiobookConvertforMac.dmg
Step 2. Add iTunes audiobooks to TunesKit
The iTunes audiobooks are encoded as M4A/M4B format. Click "Add Files" button, then you can import iTunes M4A or M4B audiobook files to TunesKit from iTunes library.
Step 3. Choose output format as MP3
Click "gear" icon next to the audiobook file name, then you are allowed to choose output format as MP3, M4A, AAC, WAV, WMA, FLAC. Of course, MP3 format is the best choice for Amazon Kindle Fire.
Step 4. Start to convert iTunes audiobooks to Kindle Fire HD.
Click "Convert" button to start converting iTunes audiobooks to unprotected MP3 format. After conversion finished, then you are free to put the MP3 files to Kindle fire and play these audiobooks on Kindle fire successfully.