How to Redo and Undo                       

You can use CPDFViewer's UndoManager class to redo and undo. The following code will show you how to do this.

if (viewer.UndoManager.CanUndo)
{
    viewer.UndoManager.Undo();
}

if (viewer.UndoManager.CanRedo)
{
    viewer.UndoManager.Redo();
}