Apologies for the trouble, can you provide some sample rich media PDFs with which you are facing this.Autumn commented
I am having the same issue. attempting to input a 3D file. It is a U3D file that was created in CAD (solidworks), exported as an .stl, opened in meshmixer, exported as an .obj, then opened in photoshop and exported as the U3D file.
For what its worth I exported a powerpoint presentation as a .pdf and that file was able to input the rich media U3D file just fine however the pdf I need to input it on is an engineering drawing exported as a .pdf from my cad software (solidworks). Not sure if the origin of the pdf has anything to do with this but I've tested several pdf's exported from the cad program and they all crash when I attempt to add the rich media U3D feature.
For reference I am working on a PC and all files were generated on a PC.