Dynamat will NOT replace the foam in the door panel. While the foam does help with sound insulation, I found it also helps heel the panel from flexing too much. If you remove the foam, you'll likely get a creaky panel whenever you put your arm on it.
You can cut off the plastic sheet glued onto the door - that's there for sound insulation only.
I personally recommend Cascade Audio for sound insulation - it's thinner, molds to the shape of the door better, and dampens the sound better. Though it is more expensive.