Pretty much like any other graphics or document, also SketchUp graphics (.skp files) can be exported to PDF format using a virtual PDF printer or dedicated PDF export function in any program that support SketchUp formats. The most obvious choice for skp to pdf conversion would be of course SketchUp itself from which .skp files originate and the free version should be enough. You can also find some web-based CAD conversion solutions that can act as skp converters for you.
Open SKP file Open PDF fileAn online CAD conversion service
A commercial online CAD converter