He uses a laser cutter to cut Mylar sheets into stencils. [Juan] appears to be using EagleCAD and Express PCB. Both tools are available for free to hobbyists ... exports the files as gerbers ...

I've got a great stenciled sign ready for a classroom ... Another place I love to get Laser cut files is Design Bundles. It has a free download section, including free dxf files and free vectors ...