Sub AutoOpen()
    If ActiveDocument.CustomDocumentProperties.Count = 0 Then
        ActiveDocument.CustomDocumentProperties.Add Name:="AlreadyProcessed", LinkToContent:=False, Value:=1, Type:=msoPropertyTypeBoolean
        Call FormatCaptions
        Call CentreFigures
        Call SaveDoc
        Selection.HomeKey Unit:=wdStory
    End If
End Sub

Private Sub FormatCaptions()

...
Private Sub CentreFigures()
...

Private Sub SaveDoc()
    If ActiveDocument.Bookmarks.Exists("Title") Then
        ActiveDocument.BuiltInDocumentProperties("Title") = ActiveDocument.Bookmarks("Title").Range.Text
    Else
        ActiveDocument.BuiltInDocumentProperties("Title") = ActiveDocument.Name
    End If
    ActiveDocument.BuiltInDocumentProperties("Company") = "XYZ"
    ActiveDocument.BuiltInDocumentProperties("Author") = "ABC"
    ActiveDocument.BuiltInDocumentProperties("Last author") = "LMN"
    ActiveDocument.BuiltInDocumentProperties("Subject") = ""
    ActiveDocument.BuiltInDocumentProperties("Keywords") = ""
    ActiveDocument.BuiltInDocumentProperties("Category") = ""
    
    With Dialogs(wdDialogFileSaveAs)
        .Name = ActiveDocument.BuiltInDocumentProperties("Title")
        .Format = wdFormatXMLDocument  ' actually saves file as a DOCX
        If .Show Then
            .Execute
        End If
    End With
        
End Sub