Resistive touch and Capacitive touch will operate the apps the same way, the same way a laser and a mechanical mouse are two different technologies designed to do the same thing for the user. Both have their advantages and disadvantages, for instance try using your capacitive iphone screen with gloves or finger nails, it wont work. A capacitive screens are known to be more accurate in general, although some nokia n900 users would argue that point. If you are buying a cheap tablet, I would not expect a resistive screen to be as accurate or responsive as a capacitive screen used on most mainstream models out there.
You should be able to pan zoom even if the screen only supported "2 points" multitouch I wouldn't stress about that. All PDF viewers will be compatible its a matter of trying a few out for yourself one by one, probably start with the official Adobe PDF Reader and go from there, everyone will have different tastes in what they want from a pdf viewer app.
Keep reading if you are still interested, http://en.wikipedia.org/wiki/Touchscreen#Technologies