I did a small python program to generate a pdf file (with one or two pages) from a kicad pcb file, which contains files for DIY fabrication (copper and masks layers). By default copper layers are negative, masks are not, and Top layers are always mirrored. The biggest feature of the code is to combine artworks on a pdf page, to avoid wasting transparent sheets. It’s a python command line tool, you can change a few options the classic way (
--no-mask for example), use
-h to get all the options.
You can get more explanations on the Gitlab snippet page.