This free extension for Inkscape makes it easy to create a solder paste stencil for soldering SMT/SMD components to a PCB.
Commercial PCB stencils are laser cut from steel, but for prototypes it's quicker and cheaper to cut your own stencil with a hobbyist-grade laser cutter or a bladed Silhouette machine. I've found 200 gsm vellum paper works well with solder paste, cuts cleanly, very cheap, can be cleaned with isopropanol (isopropyl) and reused to paste up to 10 PCBs.
The extension ONLY works with the open-source KiCad EDA, as it relies on the export SVG feature. If your PCB was designed with other software, use KiCad to import your paste file (Gerber format, .gbr or .GTP) and then export it as SVG.
I am amazed how the CAD/CAM community uses Inkscape's capabilities to solve such production problems. I could have used this a decade ago for prototyping/small batch runs. Commercial PCB stencils are extremely expensive for prototyping/small batch runs.