Is it permissible for an employee who travels to other countries for work, and is compelled to exchange currency in the black market due to the high exchange rate there, to record the official exchange rate (circulated in banks) for the company and keep the profit difference resulting from exchanging currency in the black market, whether the company is aware of this or not?

It is not permissible to record exchange rates for the company other than those at which the transactions occurred, as this constitutes forgery and contradicts reality, unless you inform the company of this and it authorizes you for the difference. Otherwise, it is not permissible for you to conceal the true exchange rate, because it is deception and forbidden forgery. Allah Almighty said: "So avoid the uncleanness of idols and avoid false statement" (Quran 22:30). And the Prophet, peace and blessings be upon him, said: "Whoever deceives is not one of us." He also forbade false statements and false testimony.