Latest questions about "file type"

I've been trying to work out how to fix this problem for nearly a month now. As the title tells, whenever I drag a video file to Handbrake, it comes up with Scan failed: unrecognized file type.

How can I open files with PS extension?

What audio software can I use to play any type of songs?

I have misplaced the encrypted file generated from this program for my last mortgage account correspondence. What is the file type (suffix) so I can search my computer for the file?