Are the amounts I took from the company's custody without right—by overstating actual expenses or writing a larger amount than what I paid to facilitate work—considered theft, and how can I return them when I don't remember the details? And are the amounts I paid to facilitate work considered bribery? And how can I repent from these sins, and will my other deeds be accepted?

The amounts exceeding the company's operational needs, which the questioner falsely reported, are ill-gotten gains (haram (definition) wealth) from which one must repent and return to the company. As for the amounts paid to facilitate work and information exchange, employees are not permitted to take them; they are illicit gains (suht). If the questioner's refusal to pay them causes him harm or injustice, then there is no blame upon him for paying them, and the sin rests solely on the recipient. Otherwise, they are unlawful (haram) for both the giver and the receiver. Repentance and good deeds are accepted if their conditions are met.