You can use special plugins for SktechUp, that allows users to import back their STL models that were previously exported with the program. Probably the easiest choice for this conversion, although it may be possible in other 3D modeling programs with SketchUp support.
Convert Stereolithography CAD file to SketchUp graphics.
We have found 3 software records in our database eligible for .stl to .skp file format conversion.
Microsoft Windows software - convert stl to skp on Windows
A software suite used for 3D CAD/DCC + Animation/Model/NURBS/Skinning translation, optimization and viewing.
Convert from stl file
to skp file
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned stl to skp. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A dedicated CAD converter for Windows, Autoconverter supports transformation of several 3D formats between different formats.
Multiplatform software - convert stl to skp on any platform
SketchUp STL is extension for SketchUp modeling tool that allows users to import and export stereolithography CAD files for 3D printers.