Thank you for your replies. Being relatively new to Android, I wouldn't even know how to
attempt this. I thought I'd just be able to locate where the app is on the device (like you would on a traditional computer), and that's it. Apparently not.
If anyone could help me retrieve the background images from Moon+ Reader Pro, please let me know. Or, would that violate a copy-right?
Actually, I'm primarily interested in
one of them -- my favourite day mode background texture, pictured below. It's that "greasy page" design. Perhaps I could write to Moon's developer directly, asking him if he couldn't let me have the picture file, if it's OK with him.