Can I convert from brake pads to disc

I am assuming you are looking to replace rear drum brakes with rear disk brakes. It is my judgement that this is not a financially feasible thing to do, because it also affects anti lock brake system operation. If it were a much older vehicle, then technically you could find a suitable donor salvaged vehicle where you could swap all related components: backing plates, parking brake mechanisms, calipers, rotors, pads, hoses, proportioning valve, master cylinder, and so on, and maybe have a fighting chance. But today's cars and trucks -- I wouldn't do it, too much to go wrong with a safety related area.