HI Frank,
Welcome to our Invigorated world!
Here’s a short recipe to make it happen. Create a small primative cube which will eventually be your invisible hinge. (It could be any shape, but a smal cube will probably be easiest.)
Assign the cube to an empty set. The first object assigned to an empty set determines its pivot point.
Now assign your book cover to that set. As you’ll see, the set now pivots on the center of the cube, not the cover.
At this point, you can turn off visibility of the cube. If you later need to adjust the placement of the pivot point, you can turn visibility back on.
You can do the same thing for other pages and animate the separately, using some of the remaining availble sets. Either create new cubes or move the one you’re already using from set to set, after you’ve added the other elements to those sets.
Hope this helps.
Have fun.
Jon