Poor display quality, great print jobs

Does anyone know how to get PDFCreator pdf's to look good on a computer display? Some of the lines and text are nice and dark, while others are all washed out and grey. The same pdf prints out great.

I changed the resolution and settings in PDF format without any improvement in quality.

Note: This is printing from Autocad. Printing from other apps results in a nice display quality.

Thanks!

Chuck