Open the PDF in Photoshop and rasterize it. Save either as a Photoshop PDF or a TIFF file with LZW compression.
8.1? Hmm… that’s pretty old for a Mac system.
Either way, he should be able to read it then. I don’t remember what the ‘latest’ version of Reader was that worked on system 8.
However, know that if it needs to be a quality pdf file, then better settings will have to be used.
If you’re on XP, try embedding postscript fonts instead of TrueType. Mac didn’t play well with TrueType fonts until sys 9.2. ..in terms of fairly stable. That might be his problem.