VectorWorks has this built-in to the program. However, I'm not sure if it's as good as a dedicated converter. It also depends how the PDF file originated. If it was created from the CAD application, it should have the vector data embedded in it, to allow conversion fairly easily and accurately. However if it was scanned, or created as a bitmap image, it's a bit harder. You'll need to use a bitmap tracing application. The free, open source multi-platform application Inkscape has a really good bitmap tracing algorithm, but there are other professional tools that can do it for you. This is harder and less accurate, and the resulting files won't necessarily be 'clean' CAD files. By this I mean that the lines may be made up of lots of little line segments, resulting in a large file that is much harder to use.
In addition, when you copy and paste, these can get embedded into the drawing. There are two ways to solve this problem. A good way is to use a free drawing app instead of an app designed to convert CAD objects and line segments into shapes. If you use Apple's Sketch, they have a great free vector drawing tool with a wide range of drawing methods. To import a CAD drawing and apply your own line segments, it is best to draw at 100% scale (this is easier to find and adjust in the first place), and in a vector data format, such as SVG (scalable vector graphics). You can change the color of your lines to make them stand out, and you can also apply a 'widen' effect to your lines. If you use a CAD app that doesn't provide a vector data format (such as.