Actually, I would rather not do that at this precise moment in time because it is a power bill from my electricity provider. (Not exactly trade secrets, mind you, but sensitive, none-the-less!)
Your most excellent suggestion did, however, remind me of another troubleshooting step I should take. That of trying another PDF document! I did just that, and the second document actually loaded without issue. That tells me that, most likely it is the original document which failed, NOT the Affinity Publisher software itself. As I live in the U. S. A., and the parent company of my electricity provider is actually a company residing in Spain, I now suspect that the issue might be a font or two that the Affinity Publisher might not have installed. The three PDF's that did fail to load were all of the same origin and type. Of course, those bills would not be coming directly from Spain, but the parent company might have forced my provider to be using a proprietary PDF software which might not be a good fit with Affinity (and possibly with the PDF standards).
Thank you, Wosven, for reminding me to be thorough in my troubleshooting procedures, and for taking the time to respond to my inquiry. It is much appreciated!
Gerra