Joe, I use a different CAD program, but TC probably has the same tools I use. I am basically self-taught, so there are probably easier ways. Be forewarned, it is a tedious project.
First I scan the plans and import to the program. Then I place loci along the curved part I want to copy. I have a tool that fits a curved line to any number of points. I use this tool to connect the loci and then see how well the line matches the pdf line. Then I nudge the loci to where a better fit would be obtained, delete the first line, and reconnect the "dots." I repeat until I am satisfied with the result.
Chuck