The only way I've found to successfully complete this operation is by converting the .pdf to a .tiff using Adobe Acrobat. We've done this a lot with details downloaded from the net where cad .dwgs are not provided, only .pdfs, and it works well. FDOT has all their details in .pdf and they reproduce well thru this method digitally and on paper.
It sucks if you need to modify the detail though. Then you have to pretty much draft it all out unless you know someone who already has it and would be kind enough to give you a copy.
Don't know if this was mentioned or not, but it depends on how the pdf was created. If you have Adobe Illustrator, it can save pdf's directly to dwg format. That works, and brings the items into autocad in a somewhat editable format, not the nicest thing, but definitely better than trying to create it from a tiff or jpeg tracing.
A lot of items will some in as splines, but I haven't yet found a way around that.
