Starting in V8, the PDF iFilter file is bundled with Adobe Reader. To get the iFilter, you need to install Adobe Reader (8.0 or higher) onto the WSS server that will be doing the indexing.

The procedure below wouldn’t work for 64 bit servers. You can find comments on this  in: http://workerthread.wordpress.com/2008/07/18/adobe-reader-9-available-works-fine-with-sharepoint/ WSS needs to know what extension to use, so you need to change a few registry entries.

In regedit:

• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\12.0\Search\Applications\{ANYGUID}\Gather\Search\Extensions\ExtensionList
  
  Find the highest number in the list and add the next value with PDF for the value.
  
• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\12.0\Search\Setup\ContentIndexCommon\Filters\Extension
  
  This is the list of file extensions with a class ID for the iFilter used to index the extension. If .pdf is not listed, add it. It should have a multi-string value in which you need to add the CLSID for the iFilter added by Adobe Reader.  In version 9, this file is called: "AcroRDIF.dll."
  
  CLSID for 9 = {E8978DA6-047F-4E3D-9C78-CDBE46041603}.
  
• Add its path to the environment variables of the server: Start Menu / right click My Computer /select Properties /go to the Advanced tab /click on the Environmental Variables button and scroll down the Path variable, select it and click on the Edit button and add the path ";C:\Program Files\Adobe\Reader 9.0\Reader" then click OK to apply and close.
  
• Reboot the server. It may take some time until the PDF documents are indexed.
  
  You can also run the search service: stsadm -o spsearch... for WSS and SSP Full Crawl for MOSS.