Apologies for not replying before. I installed Windows 8 Pro but not (knowingly) the AMD driver. Automatic screen rotate worked. But after a week or so I didn't need that function, and when I wanted to use it again just a few days ago it had stopped working. I then reinstalled the device driver, plus the AMD driver - which Windows thought had already been installed. There was a moment of excitement when the screen changed from landscape to portrait, but there it stuck. I re-set it to landscape using Control Panel/Display. There I noticed that Windows 8 doesn't give an option for variable orientation: it wants you to tell it either portrait or landscape. So it seems I can change the orientation manually but not automatically.
Member RevoMaxx is quickly moving up the ranks of Acer Community. He joined us in September and is already making a difference. It's great to see new members like him make a difference only after a few months. Thanks RevoMaxx!