Our friend the iFilter has always been a tough installation...it requires the installer to jump through hoops having to execute steps in an exact order, change registry settings and other random stuff. You can see my love/hate relationship for iFilter with SharePoint 2007 (and instrustions!!) here: http://www.rightpoint.com/community/blogs/viewpoint/archive/2010/03/18/pdf-ifilter-i-love-you-i-hate-you-ohhhh-i-love-you-again.aspx

I was hoping that the 2010 iFilter installation was easier...and it is, but there are still a few tricks.  This handy dandy article from our pals at Microsoft gives us everything we need to know (and we don't have to chase links for any additional instructions): http://support.microsoft.com/kb/2293357   ...here's my consolidated version:

1. Add pdf to file types to search settings in Central Admin
   1. Central Admin --> Application Management --> Manage Service Application
      1. Search Service Application
         1. File Types
         2. Click “New File Type"
         3. Type in pdf
         4. Click OK
   2. On EACH SERVER in the environment
      1. Add the PDF Icon to the 14 hive
         1. Add icpdf.gif to the following location on all WFE’s (you can dl it here: http://www.adobe.com/misc/linking.html)
         2. \\SERVERNAME\c$\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\IMAGES
      2. Add the following to DOCICON.xml to the following location on all WFE’s
         1. <Mapping Key="pdf" Value="pdf16.gif" /> .      
         2. \\SERVERNAME\c$\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\XML
2. Install iFilter and update registry
   1. Run the installation file on each server in the farm
   2. Update the registry on each server in the farm
      1. Navigate to the following location:
         1. HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office Server\14.0\Search\Setup\ContentIndexCommon\Filters\Extension
         2. Right-click > Click New > Key to create a new key for .pdf
         3. Add the following GUID in the default value
            1.  {E8978DA6-047F-4E3D-9C78-CDBE46041603}
      2. IIS Reset
3. Start Full Crawl
   1. Central Admin --> Application Management --> Manage Service Applications
   2. Search Service Application
   3. Click “Content Sources”
   4. Select the appropriate content source and start Full Crawl