Thank you for your reply, Svante.
At different times I’ve tried different encryption software, and it’s possible that I once had “Advanced Encryption Package” on my computer. It’s not there now, so I don’t see how it could have intruded itself into my work with Axcrypt.
The problem is that when I tried to decrypt files encrypted by Axcrypt, that strange file extension was added, presumably by Axcrypt. I don’t know how else the aep could have been inserted; these were files encrypted by Axcrypt, and Axcrypt is the program that tried to decrypt them for me. They are now “alien” files that Axcrypt doesn’t recognize. Neither does any other program I’ve tried. (They were originally Adobe files, but Adobe can’t open them now.)
I don’t see a way to attach files in the program I’m writing in. So I’ll have to settle for reproducing for you the extension of one of the “alien” files: File Name.pdf-aep.axx
This strange extension appeared when I asked Axcrypt to decrypt the file.