Hi Wajihuddin Khan,
We try to keep the WPF and Silverlight versions in sync and most of the features work identically in the two controls.
Tracking changes to the document is not available in either version. The feature has not been scheduled yet, so I cannot provide you with a specific timeline of when it will be possible to track the changes in a RadDocument.
All the best,
Iva
the Telerik team