When I open Directory Opus and click on a PDF, there is no view in preview pane, but if I click on another pdf, I can see the contents of that pdf. Then I can click on the first pdf to see what is in the document. Why does that happen? I am also finding many PDFs are not showing the preview pane contents - it has been getting worse over time. I am also now having similar problems with word documents. It is a hassle having to open each document to see what is in them. Any ideas?
Is your PDF viewer working in File Explorer's viewer pane?
If not, the issue is with the PDF viewer, not Opus itself. Windows 10 and 11 come with one built-in these days but the registry settings for it can be broken by other PDF software. Usually, the last PDF viewer installed or updated will be the one that Opus and File Explorer use in their viewer panes.
(Not all PDF viewers support viewing via the preview pane, but most do these days, including Adobe Reader, PDF-XChange, and so on. In some cases, such as Sumatra, it's an option you have to turn on during installation.)