PDF files are not being indexed by Foxit PDF IFilter. Keywords located in a PDF are not searchable from within the Archive Manager website.
From the Foxit Technical FAQ:
If you installed the Foxit PDF IFilter on your search server, the IFilter does not work after you install a Microsoft update. It is because that the upgrade program automatically overwrites the registry value of Foxit PDF IFilter with that of Adobe PDF IFilter.
Resolution 1
Uninstall Foxit PDF iFilter and install Adobe Reader 9 (if Archive Manager is installed on a x86 O/S) OR Adobe iFilter for X64 (if Archive Manager is installed on a x64 O/S).
Resolution 2
Run the Foxit IFilter MSI program again and select the repair function.
Reported for Foxit PDF IFilter 2.1.2.2301
Why can't Foxit PDF IFilter work after Microsoft updates? Do I have to re-install it?
http://www.foxitsoftware.com/support/showfaq_ifilter.php#ifilter_12
How to verify the correct installation of Foxit PDF IFilter?
http://www.foxitsoftware.com/support/showfaq_ifilter.php#ifilter_03
Which tool can be used to test the content extracted by Foxit PDF IFilter?
http://www.foxitsoftware.com/support/showfaq_ifilter.php#ifilter_27