You might have more responses if you posted this in the MS Word forum, instead of the Ribbon forum

More Word guys hang on there


But try something like this

Option Explicit
Sub demo()
    Dim sDoc As String, sXls As String
    Dim i As Long
    
    sDoc = ActiveDocument.FullName
    i = InStrRev(sDoc, ".")
    sXls = Left(sDoc, i) & "xls"
    
    MsgBox sDoc
    MsgBox sXls

End Sub