Several people have already said it: PDF's always look exactly the same on every computer they are displayed on, and they can be displayed on pretty much any computer. If Adobe's viewer isn't available for your system of choice, xpdf or some other open source viewer probably is.
And don't get me started on the evils of Word documents. Aside from the fact that they can only be displayed on whatever systems M$ decides it gives a damn about (i.e. not Linux, BSD's other than darwin/ppc, BeOS, etc), they are dependant on the fonts and screen resolution of the system they are viewed on, and of course, M$ changes the format every other month so if you managed to hack together a viewer for your favorite platform, it's worthless before it ever gets put to work.
Anyone who sends me, or referrs me to a Word document agrees by doing so to be hung by their testicles with rusty fish hooks.
BTW, before you tell me to get a 'doze Word viewer and run it under Wine, I already do that. However, the most recent viewer available is for Word 2000 docs, and it doesn't work very well. Images don't render and much of the page gets cut off for some reason.