Hello @imn
Unfortunately, to my knowledge, this is not possible to Geotag your PDF in C3D. The Georeferenced DWF would be the best alternative solution I have to provide for the problem.
@M_c3d suggestion on exporting points and importing them into the GPS software on your mobile device could also offer an alternative solution as well. Something worth looking into depending on what you are trying to achieve.
You're also welcome to share this ideal on the AutoCAD Civil 3D Ideas for future product features directly with the AutoCAD Civil 3D team and collaborate on existing suggestions with your peers and if you have additional comments specific to the software or its functionality for future consideration, please use the Product Feedback page. How to provide feedback on Autodesk products goes into more detail.
Best Regards,
Wendell
Wendell BushCivil Infrastructure Technical Support Specialist