PDF files are great for sharing data, but without additional software tools besides the ubiquitous Acrobat Reader, there isn't much that can be done with a .pdf file short of viewing and printing. Over the years, several tools have been developed to turn data from a .pdf file into a workable vector equivalent.
A free online service is available to take your .pdf files and email back a .dwg file. I haven't tested it myself, and even though the terms and conditions and privacy policy of the website seem to protect my assets, I can't believe that the ads alone on the website completely fund the process. Maybe I'm just cynical.
If you lost the source document that created the .pdf file and don't feel like manually recreating it, try ConvertPDFToAutoCAD.com.
Source:
http://cadpanacea.com/node/424