Returns or sets the distance (in points) between the bottom of the text frame and the bottom of the inscribed rectangle of the shape that contains the text. Read/write Single.
Example
This example adds a rectangle to myDocument, adds text to the rectangle, and then sets the margins for the text frame.
Set myDocument = Worksheets(1)
With myDocument.Shapes.AddShape(msoShapeRectangle, _
0, 0, 250, 140).TextFrame
.AutoMargins = False
.Characters.Text = "Here is some test text"
.MarginBottom = 0
.MarginLeft = 100
.MarginRight = 0
.MarginTop = 20
End With