Is it permissible to purchase materials not belonging to the company with my own money, then sell them through the company while giving it a percentage of the profit, and obtain the remaining profit from another company with which an agreement has been made?

An agent is not permitted to sell goods purchased with his own money through his company without its knowledge and permission, even if he gives a percentage of the profit to it. This is because an agent is obligated to act within the bounds of the agency and is not allowed to contravene his principal. He is entrusted with acting in the best interest of the principal. The company might not agree to such an act due to the competition and harm it could cause to its own authorized products.