>What you says is right. But can you guide me about using API aproach for undo, redo revert buttons.
>I want in my form is one Undo button which will be disabled. Whenever any person does changes in field, that undo button should become active. same like undo option in menu. ie whenever that undo button active, my undo button also should become active.
>Please guide me on this.

No I can't guide you through API approach, I'm not that skilled, but I can guide you through Fox way, if indeed that is what suits your need.