This must be too easy, if only it wasn't for
the vicodin...so please be patient with me ;->

Private Sub CommandButton1_Click()
system("pdfFile.pdf")
' or "docfile.doc"
' or "file.html"
End Sub

The external files will be distributed with the workbook, so I'm
not concerned about path relativity, though it would be nice to
be able to throw a msgbox just in case the file is not present in
the same folder as the workbook, or in the unlikely event
a suitable application is not available.

TIA - Lynn.