An index collects together all the text in the document. But it does nothing to change the contents of pages. So if a scanned page has no text before, it has no text after and you have an empty index.
What you are probably looking for is OCR. Acrobat can do that. Do it before indexing.
I did finally find a document to describe the OCR features. That works
for the search feature, but is there any way to add a physical index at
the end of the .pdf file?
There are three kinds of index I can think of. Let's see:
- Acrobat's index is a hidden list of words that is used to make searching faster. No way to see it on screen or a page.
- A book has an index of relevant words and terms. Selecting what goes into an index is a fairly skilled process; too large or too small is pretty useless to the casual user. An index can be created semi-automatically with a tool like Word or FrameMaker, by the author defining terms to be indexed. (Traditionally, "indexer" was a profession, quite separate from authoring).
- Some documents have automatic lists of all the words, and their count or where they appear. I believe this is properly called a "concordance". It's entirely possible to automate generating a concordance, but they are so useless/specialist that I don't know if anyone bothers to sell a PDF concordance maker.
I was hoping to preapre an index process similar to that in Word, but I
don't believe it is feasible in this scenario. Thanks for the data.
You would basically have to save as to a doc file and then process that. However, getting a reasonable DOC file from an OCR'd document is a luck of the draw. You might try it. You would basically be recreating the document. Generally the best way is to see if you can get a copy of the original document.