Hi Paul,
I got an error message when creating a 3D PDF with your dataset:

Then I tried to only export the objects in the image-covered area into a DWG, re-import it to a brand new project. This time it worked, and you could find the PDF as attached.
I have a feeling that it didn't work in the original dataset because it covers a large extent. If you look at the scale below, one of the baselines is over 10KM long. Since 3D PDF Creation doesn't allow you to select a subset of the dataset, maybe TBC cannot host such an extent in a PDF.
I will bring this to our engineers and find out what the root cause is. But at the same time, you could use the attached 3D PDF as a temporary substitute.
Hope it helps. Thank you.
Rui