I applied undo / redo for a WPF application and finished publishing my undo / redo code to http://muf.codeplex.com/ . You can also get it through NuGet. Just search for "MUF" or "Monitored Undo Framework". It includes support for Silverlight 4.0, as well as .NET 3.5, 4.0, and WP7.
WPF InkCanvas, Undo/Redo. InkCanvas . InkCanvas, , . .
Undo/Redo. "", . InkCanvas .
codeplex (http://muf.codeplex.com/). .