Adobe have made some small changes to the way that the Acrobat Reader 7.0 advanced search option works with image based text searchable PDF's.
EzeScan version 4.0.407 has had 2 small improvements made to the PDF creation function to allow it to produce PDF's that are searchable by the advanced search option in Acrobat 5, 6 or 7.
Please Note - The information below refers to a very old version of Adobe Acrobat Reader. It would most likely have no relevance if you are using a recent version of Adobe Acrobat Reader. (v7.0)