Hi. All recently noticed that PDF documents in Scribd are also SEO friendly for search engines. For example the link http://www.scribd.com/doc/17135767/FREE-by-Chris-Anderson
If you open the page and see the HTML source code, the plain text from the PDF is not presented. However if you open the cached version of the page from Google search it appears a tag html_wrapper which contains the text from the entire PDF document. Do they display different content depending of User-agent that make the request - ex. browser or bots? I've heard some SEO practices that don't recommend displaying different content for bots? How bad practice is this from SEO prospective?