Books - PDF - Preview - Search : "No Results Found" I recently upgraded from High Sierra to Mojave, and consequently iBooks became Books. I now have an issue with Books which was not present in iBooks.

I have stored many PDFs iBooks. Clicking on one of them and Preview opens. I could search in the text by Search; just fine.

Now in Books the Search in Preview gives "No Results Found" : for many PDFs but not for all PDFs. It works sometimes. (Of course I have checked that the text is present in the PDF.)

Thanks for your time.

Books version 1.16., 
macOS Mojave 10.14.2, 
MacBook Pro 13 inch Late 2013
The culprit is Preview. Also for a (text) PDF file which is not in Books the "No Results Found" message shows up. 

I killed and restarted Preview a few times on the same PDF file. And then the Search worked again.

Annoying. But it seems a solution.