The Adobe PDF plot is the most versatile format for the export of CAD drawings. In terms of its file structure when exported from CAD it is a vector-based format, which in simple terms means that you preserve the line quality. If you save or export the same drawing as a jpeg or a bitmap then these will be subject to pixilation. This is quite a common fault in raster-based exports.
AutoCAD, Vectorworks (the name gives the clue) and SketchUp are vector-based drawing programs. You can use these programs to plot/print out drawings directly to a printer and the results will be good.
A PDF, on the other hand, can be readily emailed, used in a web page, imported into page layout programs like Photoshop and Illustrator, and printed.
If your ...