Conversion of nbf files to nbs file format

It appears that both .nbf and .nbs files are from NTI Backup Now! software, albeit from different versions as well as for different purpose. It is unlikely you could somehow convert one to another, which is what nbf to nbs conversion is. If you want to recover your files, you will probably need the exact version of the program that created your backup.

Open NBF file    Open NBS file