I've had a chance to look at your PDF file and experimented a bit with various methods to maximize the quality of the imported image in DataCAD.
Your PDF document includes a full-sized sheet that when exported to a bitmap at 300 d.p.i. is larger than eight thousand pixels wide.
Unfortunately for DataCAD, that is pushing the practical limit for an imported bitmap, and 300 d.p.i. is the minimum resolution you need for a black and white image (line drawing) to be sharp enough for printing.
Adobe Acrobat does not appear to smooth (or anti-alias) the vector image when you export to a bitmap, so the 300 d.p.i. image does not look as sharp as it otherwise would. Ideally, you could export the PDF to a 600 d.p.i. image, then re-sample it down by 50% in a paint program. The result would be a smoother 300 d.p.i. bitmap. However, I get an error from Acrobat that the resulting image is 'too wide' to create.
I was able to open your PDF file in Photoshop at 600 d.p.i. and save it as a 300 d.p.i. PNG file.
The PDF does contain vectors, so if you can get a DWG file from whoever created the PDF file, that would be a better way to go.
If you can't get a DWG file, and you need to import these types of files into DataCAD often, you might consider buying a dedicated PDF conversion program such as BackToCAD ( http://www.backtocad.com/engl/convert-p ... nline.html