My recent anatomy projects forced me to start importing my 3d models into 3d pdf documents. So I'll share with you some of my findings.
The positive things about 3d pdf's are:
1. You can import a big sized 3d model and compress it into a small 3d pdf. 40 Mb stl model is converted into 750 Kb pdf.
2. You can run the 3d pdf on every computer with the recent versions of Adobe Acrobat Reader. Which means literally EVERY computer.
3. You can rotate, pan, zoom in and zoom out 3d models in the 3d pdf. You can add some simple animations like spinning, sequence animations and explosion of multi component models.
4. You can add colors to the models and to create a 3d scene.
5. You can upload it on a website and it can be viewed in the browser (if Adobe Acrobat Reader is installed).
The negative things are:
1. Adobe Reader is a buggy 3d viewer. If you import a big model (bigger than 50 Mb) and your computer is business class (core I3 or I5, 4 Gb ram, integrated video card), you'll experience some nasty lag and the animation will look terrible. On the same computer regular 3d viewer will do the trick much better.
2. You can experience some difficulties with multi component models. During the rotation, some of the components will disappear, others will change their color. Also the model navigation toolbar is somewhat hard to control.
3. The transparent and wireframe polygon are not as good as in the regular 3d viewers.
If you want to demonstrate your models to a large audience, to sent it via email and to observe them on every computer, 3d pdf is your format. For a presentation it's better to use a regular 3d viewer, even the portable ones will do the trick. But if the performance is not the goal, 3d pdf's are a good alternative.
Here is a model of atlas and axis as 3d pfg: https://www.dropbox.com/s/2gm7occq5ur50um/vertebra.pdf?dl=0