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How to fix a door
Check your strike plate.
The strike plate, or metal piece on the jam where the door latches, might be placed too low or too high. This should always be the first thing you check when identifying a door that's not closing correctly.
Look for marks on the strike plate that show the latch going above or below the hole. If you see these marks, use a metal file to file down the hole of the strike plate to make it lower or higher so that the latch can go in.