Ah, thanks. I had been misled by what it said on the DL Reader website.
I have downloaded a version to my regular Windows 8 just to test.
It does indeed claim to be the RT version, not full Windows 8.
It works for me. I can do page turns with the left/right arrows half-way up the sides of the screen.
Cursor keys don't work; which is (maybe) reasonable for an RT app; I assume swiping would work but can't check on my desktop.