Even though some search engines have started to read and Index non-HTML file formats such as Microsoft Word, Microsoft Excel, and Adobe PDF (Portable Document Format) files, none of the search engine spiders will follow links within these formats. If you want search engines to follow links on your web site, they should always be placed in your regular web pages - your HTML documents.

Do not place text in such formats if you want people to find it in search engines. At least make the content accessible in HTML format too - as a regular web page. Not all search engines will index these non-HTML formats and many will make more errors indexing them.