It you want to retrieve exotic formats like .PEF, you have to found the file format signature with a hexadecimal editor.
And, if your recovery backup software is good enough, you can use the file signature with it, then the program can recognize and recover .pef files.
More infos :
File Signatures (and many more info with google)
Edit : i open with a hexadecimal editor 3 differents .PEF files, 2 from a K200D, 1 from a K5.
They all begin with the same numbers :
4D 4D 00 2A 00 00 00 08 (maybe the 1, 2 or 3 last series of number are not necessary, it could be "
4D 4D 00 2A 00" or "4D 4D 00 2A", i don't know)
That should be the PEF file format signature.
And, as i said above, with a good recovery program, you can use it to retrieve your files.
By the way, Pentax forum, if someone could stick these datas somewhere, it could be helpful for the future.