Sub CustomWatermark()
Dim oDoc As Document
Dim oRng As Range
Dim oShp As Shape
Dim i As Long
Dim strWatermark As String

    Set oDoc = ActiveDocument
    strWatermark = InputBox("Enter Watermark")
    For i = 1 To 3
      Set oRng = oDoct.Sections(1).Headers(i).Range
      oRng.Collapse wdCollapseStart
      Set oShp = oDoc.Shapes.AddTextbox(Orientation:=msoTextOrientationHorizontal, _
                                            Left:=InchesToPoints(1), _
                                            Top:=InchesToPoints(4), _
                                            Width:=InchesToPoints(6), _
                                            Height:=InchesToPoints(2), _
                                            Anchor:=oRng)
      With oShp
        .Line.Visible = msoFalse
        .Rotation = -45
        .WrapFormat.Type = wdWrapBehind
        .TextFrame.HorizontalAnchor = msoAnchorCenter
        .TextFrame.VerticalAnchor = msoAnchorMiddle
        With .TextFrame.TextRange
          .Font.AllCaps = True
          .Font.Size = "60"
          .Font.ColorIndex = wdGray25
          .ParagraphFormat.Alignment = wdAlignParagraphCenter
          .Text = strWatermark
        End With
     End With
   Next
lbl_Exit:
  Exit Sub
End Sub