1. Download Free ifilter from: http://download.adobe.com/pub/adobe/acrobat/win/all/ifilter60.exe
You can also download Download Adobe Reader 9.0 which contains the ifilter.  Necessary for x64 bit systems. http://www.adobe.com/support/downloads/detail.jsp?ftpID=4025

2. Run the newly downloaded file and go through the install wizard with your preferences.

3. Enable the pdf extension in SharePoint. Central Administration > SharedServices > Search Settings > File Types >New File Type
4. Enter ‘pdf’ as a file extension and Click OK.

5. Right click and save the pdf icon from http://www.adobe.com/misc/linking.html

6. Add the Acrobat pdf icon to the SharePoint templates directory. Copy the Acrobat PDF picture called pdficon_small.gif in the 12 Hive\TEMPLATE\IMAGES folder, e.g. %programfiles%\Common Files\Microsoft Shared\Web Server Extensions\12\TEMPLATE\IMAGES.

7. Open the 12 Hive\TEMPLATE\XML\DOCICON.XML file.
Find the <DocIcons.ByExtension> part
Add the following: <mapping Key=”pdf” Value=”pdficon_small.gif” OpenControl=”" />
Save

8. Run
net stop osearch
net start osearch

9. Perform a full crawl to reindex your pdf files.