Rendering converts Reports from intermediate report layout to a target formats (like .pdf, .xls, .tiff etc).. In SQL Server 2008, Word Renderer has been included out of box. Custom renderers can be coded (in .net) and used in Reporting Services.
In some cases, either due to business requirements or security requirements of organizations, all of renderers should not be enabled for end users instead only subset of renderers should be enabled.
In such cases modify config file for reporting services to limit renderers.
If Reporting Services installation is in default location:
If Default Instance:
C:\Program Files\Microsoft SQL Server\MSRS10.MSSQLServer\Reporting Services\ReportServer\
If Named Instance (SQL2K8):
C:\Program Files\Microsoft SQL Server\MSRS10.SQL2K8\Reporting Services\ReportServer\
Open rsreportserver.Config File search for Tag <Render> </Render> and for those extensions that need to be disabled
For Example to disable Excel:
<Extension Name="EXCEL" Type="Microsoft.ReportingServices.Rendering.ExcelRenderer.ExcelRenderer,Microsoft.ReportingServices.ExcelRendering"/>