The Adobe PDF IFilter plug-in enables you to index PDF files in your site in Microsoft Index Server, so visitors to the site can search for text within the PDF files. By default, Index Server can search only HTML and *.doc files. To enable it to search files in other formats, Microsoft distributes filter specifications that let other developers create filter plug-ins. Adobe has used these specifications to create the PDF IFilter specifically for searching PDF files.

http://www.adobe.com/support/downloads/product.jsp?product=1&platform=Windows

http://www.adobe.com/support/downloads/detail.jsp?ftpID=2611