Shel Holtz has a great post about links and how deeplinking to articles and other types of files are still a bit of a legal question mark.
The article works on answering the question: “Do you need permission to link to somebody else’s content?”
My understanding is that, with some very narrow exceptions, any content that is freely accessible on the web is fair game for a link.
The question today, though, is whether the broad court findings on deep links apply to non-HTML content. Based on search engines’ ability to find Adobe Acrobat PDF files and the various search engines that scour images, audio, and video, it would be easy to assume that all publicly-accessible content is fair game for linking. As one court put it, if you don’t want people to link to it, don’t put it on the web