Thanks for the replies. I like the idea of an admin password. It should not be too complex to write something that enables the menus in dependence on an entry field.
I must admit I’m a bit beyond writing the concept. The current version doesn’t have room for images, although it’s a great idea. Maybe in the v2.
I attached a screenshot of the first draft. Green = completed, Yellow = Current page, Grey = not started, Orange = bookmarked.
The current version of the disabling mechanism would disable all buttons that lead to pages that are not completed, only the next page is enabled even if it’s not started.