I don't have a good answer for this problem but I do have some ramblings that might help.

To me that appears to be a document export event rather than a document save event so I'm not altogether surprised that the event doesn't get trapped by documentbeforesave. For instance, if the document is in a saved state and I make some changes and click that button and follow it through to completion, the resulting PDF has those changes but I can see the Word document is unsaved. Recording the step tells me I've run ExportAsFixedFormat.

It might be possible to handle that particular pathway by intercepting the built-in command but I couldn't find a likely contender for this.

Another alternative may be to edit the ribbon to either hide that button (FileSaveAsPdfOrXps) or replace it with one of your own.

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Andrew Lockton
Chrysalis Design, Melbourne Australia