Now stop the SynPlotService Service using ArcCatalog.

Stop ArcGIS Server Map Service
ArcCatalog then should show this:
Stopped ArcGIS Server Map Service
Now open the Service properties dialog
Next, navigate to Capabilities tab rider and check WebOffice plot extension.

Map Service capability WebOffice plot extension
Set the Layout path to the WebOfficePlotTemplates directory created before.

WebOffice plot extension capability - Set the Layout Server path
Note: The SynPlotService can be used as print service for several projects. If many prints are expected, settings concerning instances and recycle time (Pooling and Processes tab) should be revised. See WebOffice10R3_UserManual.pdf for details.
Commit the changes pressing OK.
Start the Map Service again:

Start Map Service

ArcCatalog Map Service overview