STL files used for 3D printing can be processed in a many 3D modeling programs. So it should be possible to perform STL to ASM conversion in any program that supports both of these files. Pro/Engineer and its successor product Creo Parametric should be able to translate .stl files and save them as .asm assemblies.
Convert Stereolithography CAD file to Solid Edge assembly file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert stl to asm on Windows
Set of 3D CAD/CAM/CAE design tools from PTC
Convert from stl file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.