I have a fairly large assembly that I'm trying to convert into a 3D PDF. The output is just a blank document. First it asks me to enable 3D content.
Click on Options on right side and pick either of the option. The 3d view should be visible.
Deepak is right in that you need to rust the document but you will also need to activate the 3d viewer.. I am using the Acrobat Reader DC and you can find this in the pull down menu : edit -> preferences ->
Retrieving data ...