Re-OCR pdfs in folders and enclosed subfolders

Dear DT Power users
I need to to the following task: force re-OCR on pdfs, some of which are already searchable pdfs but poorly OCR-ed. I have a general folder and many subfolders (individual applications).
I have tried to “search” all the pdfs in my folder, but when I have the list, I don’t have the option “convert to searchable pdf”, it is grayed in the “Data” menu and doesn’t show up in the contextual menu.
I have not been succesful in finding similar posts, but this is certainly because the search queries for that, pdf, ocr, etc, are too general.
Would you have solutions or suggestions? Or even a link if that was solved elsewhere?
Thanks a lot for your feedback, it will be highly appreciated,
All best

Are you running a trial version of DEVONthink?

No, I have the full purchased DT Pro Office.
When I select individually a file, I can force the ocr again, but I need to do the same thing on all the files contained in the said folder and subfolders.

PS: I have retried, if I select only a limited number of pdfs in the “search” box, it works, but the option somehow disappears (becomes gray) in the data menu, when there are too many files. I have not been able to tell what the limit was exactly. (There are bout 250 files in this folder).
If there is no neat solution, I’ll do it in several steps, but I was curious to know if I was doing something wrong,
All best

Please post a screencapture of your “search box” and results.