APD
From Just Solve the File Format Problem
APD is a format used by an emulator program to store the data contained in an APF Imagination Machine floppy disk. It contains the sequence of bits/bytes encoded on the disk.
A file is supposed to be 68K in size (though some of them seem to only be 64K), and appears to consist of a sequence of 256-byte sectors (which would make 272 sectors in a 68K file).