Hey DH,
I've been trying pretty hard to accomplish the same thing. Evidently, Adobe previously had the capability to directly import the wrl. files which are the direct output of , export to 3d from arcscene. Unfortunately with the new adobe pro they have dropped that functionality, and now it seems the only file type that is functional with 3d pdf's is ".u3d". I have also been playing with this and have found that "Meshlab" freeware will import the .wrl files pretty successfully and will also export to the u3d format. The problem i have not figured out yet is: when the .wrl file is imported to meshlab it seems to display well and the textures (i have played with lidar hillshades and aerial imagery draped on lidar dems), but when you export the model from meshlab to u3d, i cannot get it to keep the textures, i end up with a mesh surface without the surface textures. ;-( Still working on this. I have successfully added these (untextured) output files into a pdf, and the functionality seems to work for 3d viewing.
hope that moves you along a little.
cheers
Russ