The most obvious choice for any skp conversion would be to use SketchUp, because it is the program that natively uses .skp files. Unfortunately, SketchUp does not support STL format by default, which makes skp to stl conversion a little tricky.
You need to have a proper plugin installed in SketchUp; for example, SketchUp STL and SketchUp to DXF or STL plugin should be sufficient to convert any skp to stl.
If you do not have access to SketchUp, you will have to rely on third-party alternatives that support SketchUp formats.
Updated: April 6, 2024