A family of Microsoft word processing software products for creating web, email, and print documents.
I have now fixed my problem. I accessed the Printing Preferences via Settings>Devices>Printers & Scanners>Canon MX920 series printer>Manage and discovered the Page Size was set to Custom (279 by 291). I don't know when or how that happened. Setting it back to A4 fixed the problem.
I am posting this in case anyone else has a similar problem.