The publishing file format 3D PDF is not intended for backward conversions and importing to CAD applications. But if such PDF file contains U3D data (PRC B-rep), in some cases it can be convertible back to a 3D CAD model. For such conversion, you can use Adobe Acrobat 3D/Extended or e.g. the plugin SimLab 3D PDF importer for Autodesk 3ds Max.
The plug-in 3D PDF Importer [url verified 2/2017] by a Jordan company SimLab Soft is compatible with Autodesk 3ds Max versions 2010 to 2017+. It simply adds the menu item SimLab > PDF Importer to the Max UI:
By importing a 3D PDF file you can get e.g. such model (mesh data):
using the file Scheda Catalogo (3D PDF, 11.7MB)- the resulting DWG from 3ds Max: see Block library
The resulting 3D model represented in 3ds Max can be then saved (exported) to one of the 3ds Max supported CAD file formats (DWG, DXF, OBJ, IGES, SAT, VRML, etc.).
NOTE: the plugin supports only some types of PDF files, e.g. those from 3D PDF Maker, so first try its functionality on your specific files - use the trial license of the plugin.