[dad911]

I am assuming it is a flat door with veneer. And the 'windows' you are installing have trim, so the cuts should be close, but don't need to be perfect?

I would puts strips of blue painters tape on both sides of the door in the area of the cuts and press it down firmly to prevent chipping. Mark cuts, use a circular saw, finish the corners with a hand saw, jig saw, or sawzall.