There's several less-than-reputable sites that come up when you do a Google search for "Currahee Burgett pdf", I'm not going to list them here because I don't particularly support that sort of site...had to clean way too many viruses off computers after the users visited sites like that. You're welcome to try on your own, though.
I did search the publisher's site (I happen to own all four of Mr. Burgett's books, and highly recommend them to any and all), and it appears that they have not been officially released by the publisher in .pdf format. So any site you get them from will be unauthorized copies. Personally, these are good enough that I'd send a note to Bantam-Dell (apparently owned by Random-House) and see if they plan on converting these to .pdf.