APNX (Amazon Page Number Index File)
The APNX eBook file format
APNX files are often distributed by Amazon alongside with purchased ebooks in the AZW format. These files are used on Amazon Kindle devices and have first been introduced with the 3.1 version. They are known as pagination files. Especially for scientific work, this comes in handy since the page numbers on an ebook do not often match the one of the original book or paper. With the help of the APNX files, referencing the correct site number became possible by having the electronic version only.
Technical details of APNX files
APNX files help to map the page number of an Amazon Kindle ebook (most commonly in the AZW format) to the page number of the original, printed book. Users of the Amazon Kindle are thus able to see the correctly mapped page number on their device while reading. These APNX files are saved on the Kindle directly. It is not advised to open and edit these files manually.