This article explains what an AXX file is, how to decode the file so that the data is usable again, and what to do if you need to convert the AXX file.
What is an AXX file and how do I open it?
A file with the AXX file extension is an encrypted file created by AxCrypt, a program that encrypts a file to such an extent that it is unusable without first decrypting it with a specific password/passphrase.
When an AXX file is created, it is automatically given the exact same name as the unencoded file, but with this file extension added to the end. For example, encoding vacation.jpg will result in a file called vacation.jpg.axx.
You can double-click on the file to open it with AxCrypt. If you are logged into your AxCrypt account, opening the file will open the real file and not actually decrypt the AXX file.