Scanning will only produce an image or picture of each document.
The first critical point is the optical character recognition program which miraculously converts the picture into editable text.
The final point is to use a word processor (Word) which is more than adequate to carry out Finds and Searches for whatever you are seeking.
By no means cheapest but the way my computer resolves this for me is Scansoft's Omnipage v.12 and Word.
There are cheaper (and good) OCR packages just as Word is not the only word processor.