@AmandaGal, welcome to Webmasterworld! Have to ask the obvious question, you've tested the downloads from the site? Can't go by what your local dev machine displays... too much is already in cache to give good results.
Second question: Why PDF? (I use them, but I also offer an HTML version as well)
Your PDF's are really LARGE (not in words, but in non-optimzied Graphics and use of Embedded Fonts) and even over a fairly quick broadband the files hesitate or load slow... might be folks are too impatient and click the back button (Turtle 2011, example)