I couldn’t tell you at the moment Paul as I don’t have AxCrypt installed on this system.
However, where it’s stored is largely irrelevant because you can export the secret and key pair. According to this post you can go to: File | Key Management | Export AxCrypt ID Secret and Sharing Key Pair. You should then store those safely (DVD or USB locked in a safe) in the event that AxCrypt gets closed down and your computer gets lost/stolen etc.
<b>However,</b> and I’m not entirely familiar with AxCrypt’s implementation, I’m guessing you would need to re-export the ID secret and sharing key pair in the event that you ever changed your password.
Therefore you have the option to back up the credentials wherever you like; I doubt very much that AxCrypt stores it in the Windows Registry but it may be in the Windows Certificate Manager (certmgr.msc) or the hidden ProgramData folder.
If you’re desperate for an answer to where it’s stored before Svante reads this post you could take a look through the source code: it’ll be buried in there somewhere. If you do find out where, please let me know in this thread.