I think you want a very simple response but as I know this is not possible to have :-)
from the very beginning it would be good to know that OCR action is working based on page and S/W TIFF inside a Datacap application rule
Therefore you have to create and configure a Datacap application which will export your P8 document content to a batch file. The file must be converted based on Datacap other actions to TIFF s/w in your Datacap application and then runs through OCR action.
After OCR ABBYY process results a text file and HTML file for each page of your P8 document content.
After merging the html / text files of the same document content using another Datacap action (I think here you have to create on your own one...), you can import this resulting file (html or txt or both) as a new document Version of the same P8 document. Then you can use it for a search content.
I 99% sure you it exists currently nothing like this out of the box...
I developed something for a presale presentation I think 4 years ago... or perhaps more...
I hope this helps you...
Dorothea