Here is how to install it.
Install iFilter on the server that has index role assignd to it. To install just follow all the instructions here http://labs.adobe.com/wiki/index.php/PDF_iFilter_8_-_64-bit_Support
After installation, if PDF files are still not being indexed properly, sometimes server reboot will fix it.
The make sure you specify icon you want to show next to the PDF document in search result set and Document libraries.
If you have multiple servers in your farm you will have to do it for all of them.
Copy the .gif file that you want to use for the icon to the following folder on the server:
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\60\Template\Images
Edit the Docicon.xml file to include the .pdf file name extension. To do so:
Open the file C:\Program Files\Common Files\Microsoft Shared\Web server extensions\60\Template\Xml\Docicon.xm
Add the following entry:
For example, if the name of the .gif file is ICPDF.gif, add the following line:
Restart IIS server.