expression.ShowStartupDialog
expression Required. An expression that returns one of the objects in the Applies To list.
Remarks
The ShowStartupDialog is a global option, and the new setting will take effect only after you restart Word. Use the Visible property of the CommandBars collection show or hide the Task Pane without restarting Word.
Example
This example turns off the Task Pane, so it won't display upon starting Word. This will not take effect until the next time the user starts Word.
Sub HideStartUpDlg()
Application.ShowStartupDialog = False
End Sub