Just go to this link, then click Browse, select your PDF file then enter your email address.
You may have to dodge a few ads in the resulting email, but the actual DWG output is fast and the quality is not too bad.
I have posted about extracting useful data from PDFs before:
Obtain Vector Information from PDFs using Free Tools
Or if you want to convert an image to a DWG file:
Converting a raster image to a DWG file