.CDFS File

CDFS is not actually file extension and CDFS is not file format.

CDFS is abbreviation for Compact Disc File System, which is a ISO 9660 format for optical media. 

Disk images of CDFS file system are commonly stored in ISO disk images.

There is also Linux virtual file system called CDfs, but this is not actual file format as well.

How to open:

This file type is not meant to be opened directly, there is no software that could open and work with it directly, or there is no information available in public sources about opening this file type. This is usually the case of some internal data files, caches, temporary files etc.

How to convert:

You can trasnform optical disk media (CD, DVD, Blu-ray) to some kind of ISO disk images.