I think that file will be difficult to vectorize. There are lots of overlapping lines that are typically difficult for PDF-to-CAD programs to handle. You could try Scan-2-CAD http://www.scan2cad.com. They have a free trial (14 days I think) with full features enabled. I've had good luck vectorizing sketches, grading plans, contour maps, etc. When drawings get complex though, the program has had difficulty distinguishing which lines should be connected.
Do you have any kind of image editing program? If you open the PDF in something like photoshop, gimp, or corel, you should be able to save it as a higher quality image. Taking a snapshot captures the image at screen resolution and will thus be lower quality than you can get from other programs.