dwall.fas is a compiled lisp routine and can only operate within AutoCAD. Keyword: dwall.
This routine can dramatically assist architects, construction engineers and detailers. If you want a toll more simple and flexible then MLINE command for drawing your walls then give it a try. This tool is very simple to use, its goal is to help you drawing 2D layout walls as fast as possible. It draws a 2D filled up wall at your desired thickness (wall edges in WALL layer and wall fill up in SW layer). The routine stores in AutoCAD memory the last wall thickness you used, so next time you run it, the previous wall thickness value is set by default.