Backup-File Format is a data archive format used by the IBM AIX operating system.
It stores copies of files in an analogous manner to the Unix tar format.
BFF files can be created by the AIX "backup" command, and read by the corresponding "restore" command.
However, files can be identified programmatically by their "magic number" in the first 4 bytes.
[1] The Backup-File Format is also used for AIX software packages.