What is the ruling regarding the 100 dirhams taken by my friend in exchange for distributing 1000 advertisements, knowing that he only distributed 200 of them and disposed of the rest, and he cannot inform the company for fear of being fired?

Discarding the papers one was tasked to distribute is considered a breach of trust, based on the Prophet's (peace and blessings be upon him) saying: "Render back the trust to the one who entrusted you, and do not betray the one who betrays you." It is not permissible for him to take the full reward designated for distributing the papers, unless not taking the money would cause him definite harm. In such a case, he may take it outwardly and then return it to its owners in a way that does not expose him. He must also seek forgiveness and multiply good deeds.