Do I need to replace my rotors when doing my brakes on my car. on 2012 Audi S4

29K on my Audi. When doing the front brakes do I need to change the rotors as I still have 20% left on the pads.

Asked by for the 2012 Audi S4
When doing any brake service, it is mandatory for proper performance and operation to either resurface the rotors, or replace them.
Most VW/Audi/Porsche rotors call for replacement, and, especially on performance models, there are optional brake rotors that MUST be replaced when the pads are replaced to ensure simple safety.
Here is an excellent description of the service, and what it entails/what variables are present (select 'front brake service'):