Hello msteph46,
Thank you for your post.
.apk files are files that save audio wave settings for each file and are stored for purposes not to wait each time for the audio wave constructing after the file opening. This files are created when you open any new file with audio content.
You can delete these files to clean your space on computer, but note that after that if you open any file again that was previously opened (one of 77 files) the audio wave will be constucted not immediately, but after some time.