VFD (Virtual Floppy Disk)

Files with the extension .vfd are reportedly used for Microsoft Virtual PC's virtual floppy drive.

Unlike the VHD format used in the same context, these files contain no metadata; they appear to be just raw disk images (ref). So they can be manipulated the same way as those files (e.g., they can be mounted directly on Linux).

Sample files

 * Virtual PC 2007 - MS-DOS 6.22 Virtual Boot Floppy

Resources

 * Wikipedia