When you use the grouping tool on a figure's body part, import meshes into your scene or several other things, Poser stores the geometry of these items within the .pz3 itself rather then refrencing back to an .obj file. Open your .pz3 file in a text editor and look for lines 'geomCustom' followed by several lines that start with a 'v' (followed by more lines with 'vt' and then lines that start with 'f' ... this is standard obj format). This means that geometry is stored in the .pz3 itself...and if you didn't create that geometry then it would be illegal to distribute it.