Suddenly, the door shut by itself.
If 閉める is "to shut" or "to close" this is going to be the version where you don't do anything and something shuts on its own. This word is to be shut or to be closed. You know this because you put your hand in the door to open it, but then it shuts (on its own) on your hand, marring your hand forever.
The reading is the same as 閉める.