A conversion of a 3D model / CAD file is to PDF format is usually done the so called 3D PDF file. This creates a rotatable 3D preview of the model on one of the pages of PDF document. A lot of 3D modeling tools nowadays have this function, but you may also use some dedicated 3D converter for it.
Convert 3D NURBS CAD file to Adobe Portable document format.
We have found 3 software records in our database eligible for .3dm to .pdf file format conversion.
Microsoft Windows software - convert 3dm to pdf on Windows
A CAD converter with huge format support
Convert from 3dm file format
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 3dm to pdf. 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.
On-line services software - convert 3dm to pdf on web
A commercial online CAD converter
An online CAD conversion service