What is the ruling on working for a government contracting company that inflates the cost of invoices and pays differences to engineers representing government entities? Is the salary earned from this company permissible? And what is the ruling on signing these invoices?

There is no objection to working for the company and receiving its salary. It is not permissible to cooperate with the engineer in cheating, based on the Almighty's saying: "And do not cooperate in sin and aggression." The engineer must be advised and threatened with reporting him if he does not stop; otherwise, the responsible authorities must be informed. The prevailing custom of complicity with unjust engineers does not justify going along with it due to its corruption.