Even when I identified the missing font, I could stripe over the text and the Home box at the top would tell me it was Cambria - no indication that it was missing. I assume now that Word was substituting a similar font (perhaps Times New Roman). I was able to output to PDF despite the missing font. It was only when I looked at an earlier PDF of the same doc that I spotted the difference between fonts. Then I went to my font manager (Linotype FontExplorer X) I found that Cambria was uninstalled