Unfortunately trashing trashes.
Even if he was able to use a data recovery tool, unless he had done absolutely nothing since losing the file, chances are the sectors in which the document resided will have been overwritten with other data, and like the physical universe 2 objects can not co-exist in the same space.
Understand the process. Files have an address like a house has an address. Initially when you delete, only the address to the house is marked in the computer as no longer being occupied. The house stays there until something else wants to use that space then the house is demolished and another structure put in its place.
I have been in the same position and in my experience you can vainly chase your document/s, taking an enormous amount of time doing so, maybe even finding bits of it but in such an unusable form that you just get on with life and try to prepare against the same thing happening in the future.
Data recovery services with their enormous prices and sophisticated tools don't guarrantee any better results.
Peter