oPAQue (also called PAQ) is a compressed archive utility for DOS, and its associated file format. It was developed by Dmitry Dvoinikov, and distributed as freeware. It was originally named PAK.
More research needed.
IDArc interprets the first 8 bytes of a file as four 16-bit little-endian integers, adds them together, and identifies it as oPAQue if the low 16 bits of the sum equals
oPAQue files have been observed to start with
a0 38 2d 27 26 8c b7 be, which is consistent with that algorithm (sums to
But this website reports
bc 47 ce 93 40 11 e5 bd, which does not quite work -- it sums to