The problem has been solved by a friend. I had bought a new Windows 10 computer. It would seem that Windows was using its own driver for the HP OfficeJet Pro 8024, which would not print duplex. My friend downloaded the appropriate driver for the 8024 from the HP web site, which now allows me to print duplex and, more importantly for me in view of the work I do, it will allow me to print an A5 booklet from a series of A4 pages.
So the moral is, always check with the printer manufacturer that you have the right driver.
