I have a very large number of files (tens of thousands) who's binary all begins with 0x00 0x06. They do not open with 7-ZIP. I notice also that all Office files seem to share the same next 32 bytes.
It is a very old format, so I cannot find a decompression program, and do not even know how to confirm that it is the indeed an old PKZIP format.
The compressed file is indeed compressed by about 50%.