This example adds centered page numbers to every page in the active document except the first. (A separate header is created for the first page.)
With ActiveDocument.Sections(1).Headers(wdHeaderFooterPrimary)
.PageNumbers.Add _
PageNumberAlignment:=wdAlignPageNumberCenter, _
FirstPage:=False
End With
This example adds text to the first-page header in the active document.
ActiveDocument.PageSetup.DifferentFirstPageHeaderFooter = True
With ActiveDocument.Sections(1).Headers(wdHeaderFooterFirstPage)
.Range.InsertAfter("First Page Text")
.Range.Paragraphs.Alignment = wdAlignParagraphRight
End With