Saudia Flight 163 was an airplane where all passengers and crew onboard died following a cargo fire. The plane managed to land safely, and the passengers had moved to the front of the cabin. However, it is stated that:
It was noted that the doors could not be opened because the pressure was not equalized 
Why was the cabin pressure higher than outside?
As a passenger, how could you escape an airplane that is pressurized, such that the plugdoors will not open?
If you are outside of the aircraft, is there any way of opening it?