Undo and Redo Text Editing                       

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

//Undo 
if (viewer.UndoManager.CanUndo)
{
    viewer.UndoManager.Undo();
}
//Redo
if (viewer.UndoManager.CanRedo)
{
    viewer.UndoManager.Redo();
}