Is money earned from working with an electric arc, bought with a client's money after selling a product belonging to that client without his knowledge and delaying the payment of its price, considered permissible (halal) or forbidden (haram)?

Your refusal to pay the price of the door is a sin, for the price is a trust that must be paid, as Allah Almighty says: "Indeed, Allah commands you to render trusts to whom they are due." Your disposal of it without the owner's permission is an act of disobedience, and your lying is another act of disobedience. It would have been more appropriate to pay the amount or seek permission. You must repent to Allah and resolve not to return to such an act. The money you earned from working with the machine you bought with your companion's money is yours, because you are responsible for that money if it perishes, and in the Hadith (definition): "The produce is in proportion to the liability."