[bazza]

Thanks for trying to help, BRX.  Turned everything off and on again. Tried the long press in the middle: no result  Checked the Touch & Pedal Settings options: they don't refer to the central tapping area at all - which the manual says is where the various editing icons can be summoned.  I think you may be right in that this problem is with the tablet rather than MSP.  (I've also noticed that the 'sliding two fingers while squeezing them together' action doesn't compress/expand the image - which also suggests a tablet problem).

This leaves me with two challenges: the original one of how to use the 'Page order' box in the Companion screen to remove unwanted pages (since I can't access on-tablet editing), and the new one of how to get an Acer B3-A40 tablet to behave properly.  Ideas welcome.