Range.HorizontalInVertical (Word)

Returns or sets the formatting for horizontal text set within vertical text. Possible return values are wdHorizontalInVerticalFitInLine - The horizontal text is sized to fit in the line of vertical text, wdHorizontalInVerticalNone - No formatting is applied to the horizontal text, wdHorizontalInVerticalResizeLine - The line of vertical text is sized to accommodate the horizontal text.

Selection.Range.HorizontalInVertical = wdHorizontalInVerticalFitInLine