If each part is in a separate Section, you could use something like:

Sub splitter()

' splitter Macro

' Macro created by Doug Robbins to save each letter created by a mailmerge
as a separate file.

Dim Letters As Integer, Counter As Integer
Letters = ActiveDocument.Sections.Count
Selection.HomeKey Unit:=wdStory
Counter = 1
While Counter < Letters
   DocName = "Myletter" & LTrim$(Str$(Counter))
   ActiveDocument.Sections.First.Range.Cut
   Documents.Add
   Selection.Paste
   ActiveDocument.Sections(2).PageSetup.SectionStart = wdSectionContinuous
   ActiveDocument.SaveAs FileName:=DocName, FileFormat:= _
       wdFormatDocument, LockComments:=False, Password:="",
AddToRecentFiles:= _
       True, WritePassword:="", ReadOnlyRecommended:=False,
EmbedTrueTypeFonts:= _
       False, SaveNativePictureFormat:=False, SaveFormsData:=False, _
       SaveAsAOCELetter:=False
   ActiveWindow.Close
   Counter = Counter + 1
Wend

End Sub