I use PCTEX 5.1. When I print from a DVI window my embedded graphics line plots are too thin and almost fade out. When I export the document to a PDF and print it the graphics line weights are much better; however, the PDF driver actually makes every second page, text and graphics, is a little lighter. The dvi driver doesn't do that. So first, can I get the dvi driver to increase the graphics line weights, and second is there a patch for the PCTEX PDF driver problem.
I guess it's a viewer issue. There are several freely available PDF viewers available for Windows, such as
Okular and Evince are able to display DVI files, the YAP viewer too.
Finally you could check the print output. I expect the print would not show problems such as light print or too thin lines, as the software did. If your final output would be printed, consider the DVI and PDF viewer just as previewers. They are differently programmed.
I guess DVI format is an intermediate format for you, not the final, even if you publish electronically. So check the final output format. And even if you publish electonically, I recommend to check the output with different viewers, since the people who read your work may use any viewer on any operating system.
Where do your graphics come from? One potential problem are PostScript or PDF vector graphics that use lines of width 0. A line of width 0 is shown as the thinnest line possible for a given device. While this may be still enough on a display, such a line on a high-resolution laser printer is too thin to be usable. So my advice is: check your graphics for lines of width zero.