The door latch striker bolt , may be very tight , so use a six point socket or box end wrench , to loosen it from the nut plate that floats in the door frame .
EDIT: I should add that the door latch has a safety mechanism , there are two positions , fully latched and partially latched ( ajar) , if moving the striker bolt inward doesn't tighten the door up , then you might be trying to adjust for the, ajar position , and run out of adjustment . So moving the striker outwards, maybe required . Mark the start position of the washer with a pencil before you start.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.