Siehe https://www.msofficeforums.com/mail-merge/21460-multiple-page-document-individual-multiple-page-documents.html#post65503

Sub Merge_To_Individual_Files()
'Merges one record at a time to the chosen output folder
Application.ScreenUpdating = False
Dim StrFolder As String, StrName As String, MainDoc As Document, i As Long, j as long
Set MainDoc = ActiveDocument
With MainDoc
  StrFolder = .Path & Application.PathSeparator
  For i = 1 To .MailMerge.DataSource.RecordCount
    With .MailMerge
      .Destination = wdSendToNewDocument
      .SuppressBlankLines = True
      With .DataSource
        .FirstRecord = i
        .LastRecord = i
        .ActiveRecord = i
        If Trim(.DataFields("Last_Name")) = "" Then Exit For
        StrName = .DataFields("Last_Name") & "_" & .DataFields("First_Name")
      End With
      .Execute Pause:=False
    End With
    StrName = Trim(StrName)
    With ActiveDocument
      .SaveAs2 FileName:=StrPath & StrName & ".docx", FileFormat:=wdFormatXMLDocument, AddToRecentFiles:=False
      ' and/or:
      .SaveAs2 FileName:=StrPath & StrName & ".pdf", FileFormat:=wdFormatPDF, AddToRecentFiles:=False
      .Close SaveChanges:=False
    End With
  Next i
End With
Application.ScreenUpdating = True
End Sub