One way would be to add a new solid to the comp, making it the same size as the book cover. If your book cover is in a precomp, you should know exactly what it’s size is. It should be a 3D layer too. The position should be the same as the cover’s, although if the cover’s anchor point is on its left margin (which I imagine it is, so you can rotate from that point) you will need to take this into account when repositioning your new solid because the new solid’s anchor point will be in the middle.
Next, parent the new solid to the book cover, so that it automatically rotates with the cover. They don’t necessarily need the same anchor point for this to work. Then set the z position of the solid to 0.1. This will place it very slightly behind the cover. The distance should be so small that you can’t tell they’re not really touching.
Simon Bonner
youtube.com/simonsaysFX