To open s.t. (as a door, window, curtain, etc.); to leave s.t. open.
When pag (the word for when) comes before the root, the -an suffix for object is dropped even though the object remains. To leave a door or window open the prefix pa- is used and pa--un for the imperative.
When that man opened the door, he looked out and saw a demon possessed person sitting outside.
Don't leave that door open lest flies come in.