File sorting program for Windows 10

Hi all,

I have a small issue that I hope you guys can help with. We back up all our staff's data in their personal directories. Unfortunately they are not very diligent in only backing up work related items and we also have a lot of duplication of files as every time a machine is reloaded a backup is made, however they never clean out the duplicate files. My backup now stands at 6 TB - not a lot, however it does affect my offsite backup time.

My questions are: Is there a program out there that can sort files per extension firstly, and secondly, what is the best program to find duplicates.

Thanks!
Bernard