The pressurisation system will increase and decrease the cabin altitude during the climb and descent. In the cruise it's typically 7-8 psi, so there's no chance of opening a door, the mechanism will break first. However, during the initial climb out and final approach segment, if a pax was to jump out of their seat and attempt to open the door, then it would probably open (fall in only). I only know of the forward doors opening forward, (can't think of the aft doors?) so you would have to battle airflow, which I would say at 200kts+ would make it impossible to push out.