PDF is a great format to read documentation in but Adobe Acrobat Reader tends to load really, really slow. This is because Reader comes pre-installed with a load of useless stuff that loads anyway by default. This is even more annoying when you click on a PDF link in a web browser, as it will hang the entire browser. :(
Some people made the (free) Adobe Reader Speed-Up utility. In contrary to most of these "utilities" this one actually works! Reader starts up like lightning now. Really a must-have tool if you use PDF a lot.