Currently, Sitecore Content Search does not support Adobe IFilter 11 for indexing PDF files.
This is caused by general integration restrictions imposed by IFilter 11.
For general information about the IFilter integration with Sitecore, see the Developer's Guide to Item Buckets and Search document.
Sitecore recommends using IFilter version 9 instead of version 11 until the issue is resolved.
You can download IFilter 9 from the Adobe website using the following link.