If there are no images and only text, then what are you wanting to do. OCR is a process of extracting text from images. Thus there is nothing to be done and the message is giving you an appropriate comment. OCR in Acrobat will only run on pages that are a pure image. It will convert that image to text, depending on the type of OCR that has been selected (Clearscan, Searchable Text - exact or simplify graphics).
With Acrobat 9 Pro you could use ClearScan.
As with renderable characters on a PDF page, ClearScan output can undergo minor edits.
Use Examine Document to remove any previous OCR layer provided by Searchable Image or Searchable Image (Exact).
There is no practical way to "edit" the OCR output of either within PDF. Exporting to a text file gives you something to work on.
However, it may not go quickly or gracefully.
Use "working" copies (of the ClearScan PDF(s) as you practice.
For lengthy documents you might find changing the Acrobat generated font associated with ClearScan to something else that is available on the local machine.
PDF is not a "word processing" format. Never has been & won't be (its now an ISO Standard).
It does not support editing such as can be done with a word processor or page layout application.