Word it properly and then you'd be able to google. Your feedback system is called an Closed Loop Controller. That can be done with an PID controller, but you can skip letters from the "PID" if you want (lowering quality / convergence).
If you don't use PWM to controll the motor then the motor would be full speed forward, full speed backwards or stooped. It might work for your application but that would no longer be an PID, it would be an ID because the P's for "proportional" - your reaction would never be proportional. Also when people skip letters in the PID they usually skip the "I" or the "D" because the "P" is easier to implement.
