Can you use this in addition to laminate that already has a preattached pad on it?

I have read a lot of packaging and manufacturers recommendations during my purchases. They say if your laminate is pre-padded, do not use an extra layer. I think it will cause the floor to slip and create friction. The padding that the manufacturer applies should be suitable enough. You should always use a vapor barrier though (thin mil plastic) to protect from moisture. And your floor should be be free of any lumps, voids or staples and nails above grade.

Yes we have tried it but did not really feel a difference , it will void you warrenty and really it is not worth it or the expence.