I wouldn't worry about this at all.
The Samsung Touch Wiz UI looks just as pretty and is far more robust than IOS.
To give you an example, it's a pretty blatent rip off of the iphone in terms of icons and appearance, however you can add live widgets to each screen (there are 7 screens you can flick to). On one I have the weather and google live search (with voice search) in addition to my most used icons, on another I have facebook notifications open, another has a stock ticker that's always running etc etc... It actually looks far more "polished" than Iphone which is just a collection of static icons and nothing more. You can really personalize it and make it your own. The animated wallpapers are really neat too (I currently have Mario running through various levels in the background). PDF files are no problem either.
I've owned an Iphone before (although not the 4) and can honestly tell you that Android is a much better experience (if you're the least bit tech savvy, which you seem to be).
They're both winners - but if you're going to be reading PDF's the Galaxy's screen alone should tip you towards it, then you can consider the other bonuses such as the micro SD card slot, replaceable battery, not having to convert your video files etc and it's pretty much a no brainer to me. I didn't enjoy being trapped in Apple world when I had my first Iphone (the main reason I just started using my company Blackberry as my personal phone).