AutoCAD .NET :: Draw A Border Around All Entities In Drawing

I am trying to make a button such that if the user clicks it, AutoCAD will automatically draw a border that just includes all entities in the drawing.(Something) like the viewport border in the paper space)

Approach #1: The first approach could be zoom extent and draw a border around the zoomed view. how to zoom extent and draw a polyline, but can't figure out the exact size of zoomed view.

Approach #2 (optimal) : If the entity is a right circle and my AutoCAD window is not in square shape (for example, the AutoCAD window is maximized and my monitor is wide-screen monitor), Approach #1 will create redundant spaces at the right and left side of the circle entity. So if I could get the grid coordinate of far left, far right, top, and bottom entities, I can draw the optimal border around all entities in the drawing.