Docjax.com is a file based search engine, covering ebooks, xls, ppt an pdf files. It also proudly says that it provides access to 159,647+ free e-books and documents for downloading. Seemed to be a reasonable search engine when I tried it. It found almost 4,000 references to CILIP for example, but I couldn't tell you how many there were for 'National Libraries Day' as the engine doesn't recognise phrase searching, which is unfortunate. You can however limit to one file type, which is better than nothing. It's a nice idea, but to be honest, I think that I'll be sticking with a filetype: operator in the more traditional search engines. However, if you're working with students and want to make it easy for them, point them towards this one.