Doors and Windows - Exterior Double Door Catches but Can Be Pulled Open

I have a wooden double exterior door that catches when closed but can be pulled open. The alignment is correct, but the latch doesn't extend far enough into mating door. What is the best way to gain 1/8" greater penetration in the latch slot?

You have a couple of alternatives. One change the latch set to a longer bolt, or you could shim out the primary door or the semi fxed door or both.

The other thing that may help is if the semi fixed or stationary door does not already have them , slide bolts top and bottom will help keep the door in place. It could be that there is just enough movement that the semi fixed door moves with the operating door effectively reducing what penetration you may need.

Go I hope you understand what I just said. - It must be getting late.

Your right on and I will use the shimming process.