hi @Helvetosaur i dont have a 3d pdf lying around currently so no guarantee that will work, but it works on regular pdfs. i also dont know if that works on windows, but just give it a try and you have a mac either from what i remember.
change the suffix from .pdf to .zip it will change the file to a zip then extract that zip and skim through the data, maybe you are lucky and it contains the model in a standard 3d file, that may depend on how it was produced also.
3D PDFs store the data in U3D format. This utilises a super efficient compression algo that leads to incredibly small file sizes compared to the likes of DWG etc.
I looked at this a few years ago, and was able to import a 3D PDF through and old version of Adobe Acrobat Pro. They used to have a 3D plugin available for download, but this is discontinued now. The list of 3d packages that can import U3D, is short: