Hi,
here are the 2 workarounds I practised last week :
1) open the pdf in illustrator and export as DWG/DXF ---> vectorised graphic into Shark.
2) change pdf into jpg then import as a picture to re-draw on top....

JL

Hi,
It's easy (and necessary anyway) to restore the scale of a picture.
Use a reference line to match a length on the picture with scale tool...

In other words, if you have a known length on the picture, make a line on the same (real) length and scale the picture to match it.
It is visual, of course but it's the best you can do with a scanned picture...

JL

PDF is a meta format which may contain 'dumb' raster data as well as vectors.

If vectors yon can open the PDF with Illustrator or Corel or free Inkscape and export to DXF/DWG at least keeping the vector entities even if not on scale or not exactly connected. If raster data you can use it for manually digitizing it by sketching above only by scaling it roughly to a known size before. Regardless which format is used, do prefer a lossless format as PNG instead of the lossy JPEG made for photos and thus showing artefacts at hard contrasts, e.g. edges.

in general, the PDF format (compiled PostScript) has nothing to do with a CAD data exchange, it's made for transporting documents keeping their layout regardless of the used end device.