Is it permissible for an accountant to take a commission from selling software of his former company to his current company, knowing that he informed his manager about the commission after the contract was concluded and the manager was displeased by that, and is he required to inform the manager again if additional copies of the program are purchased?

If the sale occurred while you were a representative for a software company, you are not entitled to a commission unless your company authorizes it. However, if the sale happened while you were an accountant at the purchasing company and you informed them about the software without an agreement for a commission, you are not entitled to a commission, especially if this was done during your official working hours. What was taken due to the "sword of shyness" (i.e., out of embarrassment or without a clear right) must be returned. You are not entitled to a commission if the company purchases other copies unless the company assigns you the purchasing process and agrees with you on a known commission.