You don't really need a macro to do this, but the following will do it. There are however provisos and the main one revolves around how the footers are configured. There are potentially lots of footer ranges in a document - three to each section. This macro addresses only the primary footer.
Code:
Option Explicit
Sub AddPageNumbers()
Dim oRng As Range
Dim oFooter As HeaderFooter
Set oRng = ActiveDocument.Bookmarks("\page").Range
oRng.Collapse 1
oRng.InsertBreak wdSectionBreakContinuous
Set oFooter = oRng.Sections(1).Footers(wdHeaderFooterPrimary)
oFooter.LinkToPrevious = False
If Len(oFooter.Range.Text) > 1 Then
oFooter.Range.InsertParagraphAfter
End If
With oFooter.PageNumbers
.NumberStyle = wdPageNumberStyleArabic
.HeadingLevelForChapter = 0
.IncludeChapterNumber = False
.ChapterPageSeparator = wdSeparatorHyphen
.RestartNumberingAtSection = True
.StartingNumber = 1
End With
Set oRng = oFooter.Range
With oRng
.Collapse 0
.Text = "Page "
.Collapse 0
.Fields.Add oRng, wdFieldPage, , False
.ParagraphFormat.Alignment = wdAlignParagraphLeft
End With
lbl_Exit:
Set oFooter = Nothing
Set oRng = Nothing
Exit Sub
End Sub