>Couple of things
>
>(1) I use bullzip - runs on my win7 64 - http://www.bullzip.com/products/pdf/info.php

Too late. When I started writing this app, I went through half a dozen products of the kind, spent a lot of time trying them out and eventually went for the true and tried PS+GS (PDF is compiled PostScript, anyway). But I'd have the same problem - it's not that Word can't export, it can't open.

>(2) The scheduled task can be set up to run with a specific user account

It is. The trouble is that when run interactively from that account, it works; when run from the scheduler, it instantiates Word without rights.