Version:            (using Devel)
Compiler:          g++ 4.3 
OS:                Linux
Installed from:    Compiled sources

I just came across a cool feature of acrobat reader9. where you can setup in advanced search a collections.pdx (I think this is a collection of indexes of a certain pdf files).

Once the collections.pdx is added you can search from the advanced search menu 'keyword' in the collection which shows results from pdf files in the collections.

I think can be done with an extension to okular search with nepomuk/strigi backend, so you can search for a certain keyword in pdfs and pdfs from a certain root directory.