Changing file extension appearance on the fly

Hi, I recently watched this video of Forcepoint DLP. The guy over there, applied an encryption policy (which encrypts files copied to USB) to files which are on USB. In windows explorer, files are shown as not encrypted but they are actually. The interesting thing is when he ejects USB and inserts to another pc (which has no DLP endpoint software of Forcepoint), files are shown with .ws suffix. Which specification of WINAPI provides this? Thanks in advance.

Which specification of WINAPI provides this?

Huh?

Sounds like he has a file system filter driver, that changes some of the attributes of the file… particular the file extension.

Peter