In case WebOffice 10 R3 is not able to connect to ArcGIS Server properly it may be that you get error log entries in WebOffice.log like this (search for 0x80070002)
failed to get the map service xxxx@yyyy
AutomationException: 0x80070002 -
caused by : com.esri.arcgis.interop.AutomationException : AutomationException: null
Solution: Add the Windows user SYSTEM to the local agsusers group. The SYSTEM user is the Windows user executing the Apache Tomcat service.
To check if connecting to the ArcGIS Server machine from the Application Server machine (where WebOffice 10 R3 web application is installed) using DCOM, you can use the Utility provided on the WebOffice 10 R3 installation media (Software\Util\ArcGIS Server DCOM Test Utility).