Acrobat User Community Forums

If the 3D object is an annotation (which most things are in PDF), then it should work but only as long as the form isn't re-opened and re-saved in LiveCycle Designer (at which point the annotations may be discarded if they aren’t supported).

You'll have to try it out for yourself: Save the form as a PDF form, open it in Acrobat and try to insert the 3D object. Depending on certain factors, Acrobat may not even let you get that far but if it does, then try saving the PDF in Acrobat, re-opening it in Designer, saving the form again and re-opening it in Acrobat, once again.