I don't think that there would be a security issue to your site. I have .doc files allowed on my site and it always opens them in Word. I think only executable files, like .exe, .php, .cgi, etc, are a direct threat to the site.
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.