This has nothing to do with AxCrypt, and all to do with Windows and the Windows Encrypting File System that you are using (probably inadvertently).
If you do not backup your certificate, you will lose all EFS-encrypted (not AxCrypt-encrypted) data if you re-install Windows, your computer dies, reset your Windows password or move the files to a different computer and no longer have the old one available.
You can tell if your files are EFS-encrypted by looking at how they are displayed in Windows Explorer. In pre-Windows 10, the text was colored green, in Windows 10 the icons have a little ‘lock’ overlay. You can also check this by right-clicking the file, selecting properties, Advanced, and seeing if the checkbox ‘Encrypt data’ (not the exact text, don’t recall it exactly) is checked.
Once again – it’s got nothing to do with AxCrypt. It’s a built in feature of Windows. Google for Encrypting File System Windows for more info.