UI Editor & Gizmos in Runtime

We have a project that customer will make their own book. So I need to make an editor program that user will be able to edit text with gizmos and cursor in Unity Runtime. I mean that when unity game starts, there is a text, when player clicks on this text, gizmo will be active and player should change its transform and text inside textbox(like in MSWord, player will be able to select specific word and change its font, size, color etc...)

I couldn't find a good way to implement it. How can I achive this goal?