Did they have shadow copy turned on? You could use that. Otherwise, you would have to STOP all access to the server so the file is not over written (in case it was deleted) and then use a file recovery program. There are many out there that should work. If you are not a more experienced technician, this maybe way over your abilities and would require services of an expert.
So, if you do a search for the file/folder name on the server and nothing is found, there is NO ‘back door’ just skill, knowledge and the right tools to recover the folders/files.