What is the ruling on things found by a worker while sorting paper, given that the employer said: "Whoever finds something, it is his"?

If your relative and those with him collect discarded papers, the original principle is that what is inside them belongs to their owners. The employer's permission for workers to take any money they find in these papers does not make it permissible for them to take it, because it is permission concerning something he does not own. This is unless it is known that the owners of the money have given permission, either explicitly or by custom.

Assuming it is not possible to identify the owners of these funds, then they fall under the ruling of a found item (luqatah).