We know of one or two sites (or many more, actually) that provide file conversions between PDFs, Word documents, and a few other files. CometDocs takes the all-in-one approach, supporting more than 50 file types.
That's a pretty catchy selling point in itself—you can convert PDFs to Excel files, huge TIFF images to PDF, icon files into images, and the site even does a little OCR work on certain image-to-text conversions. But the simple-to-use site also can take almost any file type that's lost an extension and tell you what kind it is, as well as compare two different text or document files and return the text lines where they're different. It can pull the ID3 tags off an MP3, convert an HTML file into an RSS feed, and, well, hit the "FAQ" tab below to see what else it can do.
The site's disclaimer says it will never rent or sell your email address. Signing up with an email and password gives you a "Premium Account," though it's not really spelled out what that offers over CometDocs' free conversions. Thanks Martha!