Do I need to replace rotors when I replace pads?

Not automatically. Forum mechanics generally advise measuring rotor thickness and checking for scoring or warpage; if the rotors are within spec and smooth, new pads on existing rotors are fine after a proper bed-in. If you're upgrading to a more aggressive friction compound (e.g., carbon-fiber ceramic for towing), many users pair new pads with fresh rotors to get a clean transfer layer.