The physical attacks of the creature I don't believe have to penetrate, at least regarding Parma. If you are speaking about wards however, that is another question. The exact effects of parma and ward based protections can be astoundingly debatable however and generally come down to a judgement call.
Parma I usually assume only protects you from a direct magical force. Dragon's claws and whatnot do not count. Dragon's magical attacks, like breathing fire or whatever, does... and they have to penetrate.
Warding, if it exceeds the creatures might and whatnot in order to be effective, I usually consider to provide complete protection from the creatures abilities and not to allow direct or indirect contact/force. Warding is much better than parma if you can get it to work.