Currently, there is a DocumentHistory property IsEnabled indicating whether the history for the RadDocument is enabled. This property is not working and history cannot be disabled.

Workaround:

Use DocumentHistory Clear() method by attaching to editor's CommandExecuted event.

        private void Editor_CommandExecuted(object sender, Telerik.Windows.Documents.RichTextBoxCommands.CommandExecutedEventArgs e)
        {
            editor.Document.History.Clear();
        }