If there are more than one period characters, using split creates a few more problems. It would be better to use
Code:
sFile = ActiveDocument.Name
sFile = Left(sFile, InStrRev(sFile, Chr(46))) & "docx"
'or, if you want to add some text to the end of the filename
'sFile = Left(sFile, InStrRev(sFile, Chr(46)) - 1) & "-sometext.docx"