Is the money obtained by the friend in exchange for helping the client restore his rights lawful or unlawful, and what should he do with it?

Your friend has no right to arbitrate in the dispute between the spouses regarding property entitlement; this is the judge's prerogative. Nor is he permitted to betray the trust of his work and dispose of company documents. His taking of the money exacerbates the situation, as an employee is not allowed to accept a gift from his company's clients because of his position without permission, let alone if the reason for the gift is an impermissible act. He must return the money to its owner and, if possible, return the waiver document to the company. If the client has been wronged, let him resort to the judiciary.