@errante and @Hardkorn, I got the result I wanted. I can now get the page count of PDF documents without even having to see the PDF Info windows. And I went a little further. I created another script that displays both the page count of PDF files and Office documents. This way, there's no need to have two separate columns, one for PDFs and another for Office (native to Opus).
I'm not going to publish the scripts here because I'm going to post them in the Buttons - Scripts section. Maybe they'll be useful to other people, and they'll have faster and cleaner access there. Thanks a lot!