I had great hopes for the hidden text layer Acrobat creates when OCR-ing text, but I never figured out how to get sufficient control over that text. In particular, I couldn't get corrections to work smoothly -- always a challenge when OCR-ing mixed languages, not to mention hand-written Chinese. I've heard Abbyy FineReader might allow easier access to the hidden OCR text, but I decided to try making my own text layer when digitizing back issues of a scholarly journal, Early China. Testers found Reader's menu for swapping layers awkward, so I put a button for this on each page -- actually, two buttons superimposed, each visible in the appropriate layer. This example (3.5 MB) includes quite a few archaic Chinese characters and other snippets from the scans set in-line with text in the text layer, which is practical only because InDesign CS4's export to PDF is smart enough to re-use a single copy of an image that occurs repeatedly.
In fact, I used Acrobat's OCR to recover as much of the text as it could. The copy still required extensive fixing up, nor was re-setting it in InDesign trivial. But the result does meet the goal of giving the reader both searchable text and a convenient way to check the original publication.
