Pages (particularly a multiple number of pages) are not a very good thing to
be using as a basis.  If there was some other way of determining the split
point, such as a section break, the result would be more repeatable.  You
could modify the following code to do it:

Sub splitter()

'

' splitter Macro

' Macro created 16-08-98 by Doug Robbins to save each page of a document

' as a separate file with the name Page#.DOC

'

Dim Counter As Long, Source As Document, Target As Document

Set Source = ActiveDocument

Selection.HomeKey Unit:=wdStory

Pages = Source.BuiltInDocumentProperties(wdPropertyPages)

Counter = 0

While Counter < Pages

   Counter = Counter + 1

   DocName = "Page" & Format(Counter)

   Source.Bookmarks("\Page").Range.Cut

   Set Target = Documents.Add

   Target.Range.Paste

   Target.SaveAs FileName:=DocName

   Target.Close

Wend

End Sub

The following is an untested modification of the above that might do it

Dim Counter As Long, Source As Document, Target As Document

Dim i as Long, mypage as range

Set Source = ActiveDocument

Selection.HomeKey Unit:=wdStory

Pages = Source.BuiltInDocumentProperties(wdPropertyPages)

Counter = 0

While Counter < Pages

   Counter = Counter + 10

   DocName = "Page" & Format(Counter - 9)

   Source.Bookmarks("\Page").Range.Cut

   Set Target = Documents.Add

   Target.Range.Paste

   For i = 1 to 9

           Set mypage =     Source.Bookmarks("\Page").Range

           Target.Range.InsertAfter mypage

           Source.Bookmarks("\Page").Range.Cut

    Next i

   Target.SaveAs FileName:=DocName

   Target.Close

Wend

It should number the separate files as Page1, Page11, Page21, etc.

If you had section breaks, you could use:

Sub splitter()
' splitter Macro
' Macro created by Doug Robbins to save each letter created by a mailmerge
' as a separate file, retaining the header and footer information.
Dim i As Long, Source As Document, Target As Document, Letter As Range
Set Source = ActiveDocument
For i = 1 To Source.Sections.Count
   Set Letter = Source.Sections(i).Range
   Set Target = Documents.Add
   Target.Range = Letter
   Target.Sections(2).PageSetup.SectionStart = wdSectionContinuous
   Target.SaveAs FileName:="Letter" & i
   Target.Close
Next i
End Sub