The following method re-purposes a built-in building block to add the data in the first page header:
Sub InsertDateWatermark()
Dim oRng As Range
Dim oHeader As HeaderFooter
Dim oTemplate As Template
ActiveDocument.PageSetup.DifferentFirstPageHeaderFooter = True
Set oHeader = ActiveDocument.Sections(1).Headers(wdHeaderFooterFirstPage)
Set oRng = oHeader.Range
On Error Resume Next
For Each oTemplate In Application.Templates
If oTemplate.name Like "Built-In Building Blocks*" Then
oTemplate.BuildingBlockEntries("CONFIDENTIAL 1").Insert Where:=oRng, _
RichText:=True
End If
Next oTemplate
With oRng.ShapeRange.Item(1)
.TextEffect.Text = Format(Date, "Short Date")
.TextEffect.FontSize = 24
.Height = 29.25
.Width = 102#
End With
lbl_Exit:
Exit Sub
End Sub
To remove it
Sub RemoveDateWatermark()
Dim oRng As Range
Dim oHeader As HeaderFooter
On Error Resume Next
ActiveDocument.PageSetup.DifferentFirstPageHeaderFooter = True
Set oHeader = ActiveDocument.Sections(1).Headers(wdHeaderFooterFirstPage)
Set oRng = oHeader.Range
oRng.ShapeRange.Item(1).Delete
lbl_Exit:
Exit Sub
End Sub