Microsoft has a nice feature for their word document format named "Custom Property Part". This part is designed for very good and well trained geeky secretaries that have the capability to write binaries.
From page 68 of the part1 of the specifications, 12.3.5 Custom Property Part, we can read:
This binary part supports the storage of arbitrary user-defined data.
You have 2 kind of secretaries: those who write binary and those who don't.