I don't know what engine you guys are using but I recommend using global values, like every time the player finishes a page of the book the value would update by 1 and that will save in a folder like a .ini and each number will be a specific page so when the player loads the game back in the they will be on the same page, it doesn't have to the exact spot the player left off at, just a checkpoint after each page
Heatstroke was developed in Unity.
Unfortunately on Heatstroke (and all of my projects) programming changes are outside my jurisdiction. Braden Banning is your man if you want to suggest and future changes to Heatstroke.
His personal website is linked on this page above and he can be reached at his email: Braden.Banning@gmail.com