This is what happens to me too.
I had 1 open file selected and I got the same outcome. No dice.
OCR doesn’t even show up in my Preferences. Yes, I bought the license.
You bought what license?
The person you replied to had a Standard license and I suspect you do as well.
Only the Pro and Server editions of DEVONthink have OCR built in.
Select DEVONthink 3 > Purchase to open our online store with upgrade options specific to your license.