You'd have to have a pretty specialized import tool that would take PDF and create a solid from it. That is an interesting idea though, and I wonder if anyone has created such a beast. It would definitely be a niche tool, and not a simple task to code/develop. Even having something capable of reading and
interpreting dimensioning of a 2D drawing would be a challenge to write, given all of the different ways/places/styles a dimension can be added.
[edit] I just happened to find this:
Print2CAD 2022 That app will create a DWG from PDF, but it looks to be intended for the architectural market. Even so, it might be an interesting thing to try out. I doubt it is intelligent enough to read/apply dimensions though.
A better solution might be a change to our culture. There are those that want to keep plans private for fear of having the engines mass produced in China. I get that, and I respect their desire/right. And there are those that are not concerned with the Chinese manufacturing problem and freely distribute their plans via PDF. Maybe part of the answer here is to encourage these latter folks to consider also distributing the DWG, STL, or other native format of the CAD system being used (if any). This is far less transportable, so I think it would be best to
also post a PDF, but I've often thought it would be nice
not to have to replicate a design in a CAD tool a second time. That said, redrawing in your CAD does form as its own form of validation and fosters your learning.
I also balked at the Alibre deal this time around. I came very close, but I didn't get there. I think it was the whole discussion on the MeshCAM path generation that finally pushed me to waiting. I just didn't have the time to deal with checking it out versus DeskProto or some of the other options discussed. The CAM issues combined with some of the concerns about Atom just held me back. Well, that and the fact that I was way too busy this weekend trying to fix a Mitsubishi servo amplifier for a guy. Give a dog a bone and he'll gnaw on it forever. That is the way I am with this problem... I'm doing all this for free for the guy because it is an interesting challenge, but geez! I've spent a lot of time trying to figure this last problem out!
I did put Alibre Workshop on my Christmas list though. There is a remote possibility that my family got it for me anyhow. That would be cool if they did. Despite my reservations (above), I would never turn it down, and I'd get enough value out of it (truth be told, 3D CAM is not my main interest anyhow... I've a gazillion endmills, but very few are ball type).