Catching F1 keypress

[Dell Stinnett]

How do I go about checking user input to see if the user has pressed F1? I
need to be able to redirect F1 to open a .pdf file to provide help for the
specific module the user is in - I can get the correct .pdf file, but I'm
not sure how to tell if the user has pressed F1.

Thanks!
-Dell Stinnett