Printing Grey Scale PDF's

Hello, this is my first post in BE.

 What I am having issues with is printing my documents to A1 greyscale PDF's.  I have modified the pdf.plt file to use only two pens

pen (1)=(0,2,4,6,7,8-54,56-95,97-151,153-252,255)/RGB=(0,0,0)
pen (2)=(1,3,5,54,96,152,254)/RGB=(180,180,180) ;medium grey

But when I print to PDF the file looks great on the computer but when I print it to our laser printer the grey lines print out with little dots.  I have no problem printing from Solid Edge, or AutoCAD

Is there a way to fix this?

What method do you use to create PDF's

 

Thank you,

John Matthews