Files with the .BAC extension contain the backup data of one or more files, and it can also be part of a larger file. If you divide the backup of a larger file into several smaller files, they usually have the extensions .B01, .B02, and so on.

BAC files are created using Backup Plus backup software provided by Avantrix, and their restoration was possible using the Backup Plus Restore Manager software. Currently, the software is no longer supported, but you can try to open your files using a ZIP archive program after changing the file extension to this format.