Do I need to replace rotors when I replace brake pads?

Not always. If your rotors are within thickness spec and free of deep grooving or warping, fresh pads alone are fine. If they're worn or you want a refresh, an all-in-one kit such as the PowerStop pads-plus-drilled-and-slotted-rotor set bundles both so the components are matched, which several verified-purchase buyers cite as a convenience.