I’ve been fiddling with Microsoft Sharepoint Server 2010 Foundation for a while now and was wondering, why the heck I could not index PDF documents.
I could add the PDF icon and all, but search would not work. Even if I did the same trick workaround that worked with WSS 3.x.

After a myriad of registry edits I found a working solution:

In SQL Server Management Studio open your Sharepoint 2010 Search Database (usually WSS_Search) and open the table MSSConfiguration for edit.
Insert a new row with the following values (lookup you GUID and insert accordingly):
Name: <guid>\Gather\Search\Extensions\ExtensionList\48
Value: pdf
LastModified: Current Date and Time

Restart your Sharepoint services (or the whole server). When done, start a new full crawl by issuing the following command:
"C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\BIN\STSADM.EXE" -o spsearch -action fullcrawlstart

Remember! You will need a working PDF iFilter installation (Adobe PDF iFilter or Foxit PDF iFilter).