>>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.

Can you set it to run under the Network Service account? Do you know if the Windows Server 2008 R2 is using the new managed service account?

One more weird thing which may or may not pertain in your case. I debated posting it because it's tricky. See if this is has any relation to your situation or helps in anyway (it's actually for base filtering, but I'm wondering if the Discretionary Access Control List is incorrect for your service):

http://blogs.technet.com/b/rspitz/archive/2010/09/19/quot-access-is-denied-quot-when-you-attempt-to-start-the-base-filtering-engine-service-after-upgrading-from-windows-server-2003-to-windows-server-2008-r2.aspx