See this link for details.
Adobe currently bundles a 32-bit PDF iFilter with Adobe Acrobat® 9 as well as free Adobe Reader® 9 software. It uses the Microsoft iFilter interface and allows third-party indexing tools to extract text from Adobe PDF files.
In response to customer requests, Adobe is releasing Adobe PDF iFilter 9 for 64-bit platforms, which will allow searching PDF files on Microsoft® Windows® 64-bit platforms for applications such as Microsoft Office SharePoint Server 2007, Microsoft Exchange Server 2007, and Microsoft SQL Server 2005.
Note that Acrobat Reader does not provide IFilter for 64 bit Windows by default.