Configuring PDF related stuff for SharePoint 2010 (and 2007) is very simple, yet annoying and often forgotten SharePoint configuration step. There are nice articles (link, link) to help you configure it but when you do it manually chances are you will miss configure something.
I wrote a simple PowerShell script to automate this, and it will do everything for you > configure PDF Icon and PDF crawling.
Here is what you need to do:
Grab the Powershell script and instructions over at SharePoint Use Cases