Hi Kevin,
Thank you for your interest in Syncfusion Products.
Presently we don't have support to convert RTF to PDF in Silverlight Platform. Please refer to the below link for the list of supported elements in silverlight.
http://help.syncfusion.com/ug_92/Reporting/PDF/Silverlight/default.htm?turl=Documents%2F45supportedelements.htmPlease let me know if you have any questions.
Thanks
Pradeep