To do it properly, bookmark the first instance of your date, cross-reference that bookmark for each of the other instances, and use something like the following in the 'This Document' code module of the document or its template:
Code:
Private Sub Document_Open()
If MsgBox("Run Macro?", vbYesNo, "Message") <> vbYes Then Exit Sub
Application.ScreenUpdating = False
Dim BmkRng As Range: Const BmkNm As String = "MyDate"
With ActiveDocument
If .Bookmarks.Exists(BmkNm) Then
Set BmkRng = .Bookmarks(BmkNm).Range
BmkRng.Text = Format(Date + 7, "mmmm d, yyyy")
.Bookmarks.Add BmkNm, BmkRng
End If
.Fields.Update
End With
Application.ScreenUpdating = True
End Sub