In Adobe Reader X they removed the ability to do iFilter indexing from the Windows Indexing services of PDF files. To get around this you had to install Adobe Reader 9.x on 32bit systems or the iFilter 9 on 64bit systems.
Does anyone know if Adobe Reader XI follows the same stance of not exposing its iFilters to the Windows Indexing service? I've done some searching but this answer does not seem to exist yet where I can find it.