Thanks for all the great suggestions! I tried the Comet Docs but I always get error when trying to convert the pdf to dwg. Also, there seems to be the same problem with quality when converting the pdf to image file. In the future I will be using this conversion tool for other purposes for sure. So, thanks a lot for the link.
Wintopo looks promising but the layout needs be converted to image because the software can't open pdf-file. I believe that this is the reason why contours get broken when creating dxf-file.
I don't have Illustrator and so I don't really know how well it could work in my case.
Here is the map that I am trying to trace in Sketchup:
http://www.golfpirkkala.fi/images/stories/pdf/gpi_layout.pdf.pdf