Create a directory on your ArcGIS Server machine, where the Plot Layouts files (file extension .layout) will reside, by copying the layout folder from the WebOffice 10 R3 installation media (On Installation media see WebOffice10R3-DVD\Software\WebOffice extensions\WebOfficePlotTemplates).
Note: Recommended location is <ArcGIS Server location>\WebOfficePlotTemplates
Using a subdirectory of the <ArcGIS Server location> ensures that the file system rights for accessing the plot layouts are correctly set.
The ArcGIS Server location is the root directory specified in ArcGIS Server Post Installation where ArcGIS Server put its files (images, cache tiles, job output etc.):

ArcGIS Server location