I assume the problem is to do with the fonts your printer has, and the act of converting the ps to a pdf adds the fonts necessary.
I reckon the best way to check what is responsible for poor typsetting is to try running troff's output through proof(1). It is not necessarly the nice-est looking rendering of your document - due to a lack of antialiasing of fonts I suspect, but if you zoom in the layout should accurately reflect what troff thinks it has done. -Steve
