Answer
Newton’s first law shows that you move in a straight line at constant velocity. The road exerts a force on the car, accelerating it and causing it to follow a curved path, and you run into it.
The door presses against you (action) to try and provide the centripetal force to make you follow a curved path. By Newton’s third law, the reaction force is you pressing against the door.
If the door (and friction between you and the seat) were missing, you wouldn’t make the turn; you'd continue in a straight line and fly out of the car.
