The included openscad source lets you customize the length and width of the piece. Although an stl is provided, you probably don't want to print that unless you're making a Greenleaf McKinley doll house. The finished product just slips right over the raw doorway opening and holds in place quite well - no tools required.

Note that the vertical and horizontal trims are different. The horizontal has two 45 degree cuts, the vertical only one. If you want to print a horizontal molding (ie. the overhead piece), set isHorizontal to 1. For vertical pieces (with only one 45 degree cut), set isHorizontal to 0.