.BKF file extension

This is the basic program to work with .BKF extension

Windows Backup

Windows Backup Microsoft Backup File

With solutions for both local and Internet-based backup, the ability to back up everything from individual files to complete servers (including Active Directory, Exchange and SQL Server) — both physical and virtual — and support for a wide range of backup devices, BackupAssist is unmatched for its flexibility and versatility... (more)

The program works with the following extensions: iso, gi, bkf, c2d, cue and roxio

.BKF extension is also supported by the following programs:

Dragon UnPACKer

Dragon UnPACKer Dragon UnPACKer 5 Archive

It is an open source game archive (Quake PAK) unpacking program.
Iomega Automatic Backup

Iomega Automatic Backup Microsoft Backup File