Thank you for the suggestion.
Anyone who can touch and hold Back and Overview buttons can unpin the app. Not sure how much protection it would provide.
I am currently trying Guest account without deleting previous sessions and activity. It is a bit clumsy but that way I am able to install those few apps I want to use without need for PIN or password and does not have root/admin access.
I do not know if there is an option to share files or clipboard between user and guest, but this setup is inconvenient because what I do in one profile is not available in the other, e.g. change in navigation as guest is not accessible to user and vice versa.