Hice un pequeño script con WPF para extraer el parametro comentario(Ejemplo puertas).
No puedo hacerlo,aqui estas mi codigos,que falta?

I made a small script with WPF to extract the comment parameter (Example doors).
I can't do it, here are my codes, what's missing?

class Utils
    {
        //variable
       public string Nombre { get; set; }
        public string Comentario { get; set; }
        public string Marca { get; set; }
        public string datos { get; set; }

        //public Document _doc;


        #region Seleccionar Elemento
        /// <summary>
        /// Seleccionar un elemento
        /// </summary>
        /// <param name="uidoc"></param>
        /// <param name="doc"></param>
        /// <returns></returns>
        public Element SeleccElement(UIDocument uidoc)
        {
            //Documentos
            Document doc = uidoc.Document;

            //Seleccionar Elemento en la pantalla
            TaskDialog.Show("Info_Revit", "Seleccione un elemento");

            // Access current selection
            Selection sel = uidoc.Selection;

            //Obtener la referencia seleccionada
            Reference reference = sel.PickObject(ObjectType.Element, "Seleccione un Elemento");

            //Obtener el elemento elegido
            Element element = doc.GetElement(reference);

            return element;
        }
        #endregion

        public string Getdata(Document doc, Element elem)
        {
            BuiltInParameter built_name = BuiltInParameter.ELEM_FAMILY_PARAM;
            BuiltInParameter built_Comments = BuiltInParameter.ALL_MODEL_INSTANCE_COMMENTS;
            BuiltInParameter built_Marca = BuiltInParameter.ALL_MODEL_MARK;

            Nombre = string.Format("Nombre {0} => ID {1} ", elem.get_Parameter(built_name).AsValueString(), "<" + elem.Id.IntegerValue.ToString() + ">");
            Parameter param_Commen = elem.get_Parameter(built_Comments);
            Parameter param_Marca = elem.get_Parameter(built_Marca);

            if (param_Commen != null)
            {
                Comentario = param_Commen.AsValueString();
            }
            
            if (param_Marca != null)
            {
                Marca = param_Marca.AsValueString();
            }
            datos = Nombre + Comentario + Marca;

            return datos;
        }

        public void SetData(UIDocument uidoc, Element elem)
        {
            Document doc = uidoc.Document;
            
            BuiltInParameter built_Comments = BuiltInParameter.ALL_MODEL_INSTANCE_COMMENTS;
            //BuiltInParameter built_Marca = BuiltInParameter.ALL_MODEL_MARK;
            
            Parameter param_Commen = elem.get_Parameter(built_Comments);
           // Parameter param_Marca = elem.get_Parameter(built_Marca);

           // Comentario = param_Commen.AsValueString();

            //Iniciar una transaccion
            using (Transaction trans = new Transaction(doc, "Modificar Parametro"))
            {
                trans.Start();
                //Modificar los parametros
                if (param_Commen != null)
                {
                    //Comentario = param_Commen.AsValueString();
                    //param_Commen.Set(Comentario);
                    MessageBox.Show(Comentario);
                }
                //if (param_Marca != null)
                //{
                //    param_Marca.Set(Marca);
                //}
                trans.Commit();

                TaskDialog.Show("Info_Revit", "Parametro Modificado correctmente");
            }
        }
    }

/// <summary>
    /// Lógica de interacción para MainWindow_Seleccion.xaml
    /// </summary>
    public partial class MainWindow_Seleccion : Window
    {
        //Accesos
        UIDocument _uidoc;
        Document _doc;
        Element _elem;

        public MainWindow_Seleccion(UIDocument uidoc,Element elem)
        {
            Document doc = uidoc.Document;
            InitializeComponent();
            this._doc = doc;
            this._elem = elem;
            this._uidoc = uidoc;
            Utils u = new Utils();
            u.datos = u.Getdata(_doc, _elem);

            this.DataContext =u;
        }

        private void btnGuardar_Click(object sender, RoutedEventArgs e)
        {
            Utils u = new Utils();
            u.SetData(_uidoc, _elem);
            this.Close();
            
        }
    }

....
try
            {
                Utils utils = new Utils();
                Element elem = utils.SeleccElement(uidoc);
                MainWindow_Seleccion _Seleccion = new MainWindow_Seleccion(uidoc,elem);
                _Seleccion.ShowDialog();

                // Assuming that everything went right return Result.Succeeded
                return Result.Succeeded;
            }
            // This is where we "catch" potential errors and define how to deal with them
            catch (Autodesk.Revit.Exceptions.OperationCanceledException)
            {
                // If user decided to cancel the operation return Result.Canceled
                return Result.Cancelled;
            }
<Window x:Class="Seleccionar.MainWindow_Seleccion"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:Seleccionar"
             mc:Ignorable="d" 
             Height="280" Width="420" 
             Title="Ventana de Seleccion"
             Background="Lavender" WindowStartupLocation="CenterScreen"
             ResizeMode="CanResize">
    <Grid>
        <!-- Crear filas-->
        <Grid.RowDefinitions>
            <RowDefinition Height="30"/>
            <RowDefinition Height="25"/>
            <RowDefinition Height="250*"/>
            <RowDefinition Height="25"/>
        </Grid.RowDefinitions>
        <Label Content="Editar Parametros" FontSize="18" FontWeight="Black" HorizontalContentAlignment="Center" />
        <Label Grid.Row="1" Content="Informacion del Elemento" 
               FontSize="14" Foreground="Black" 
               ScrollViewer.VerticalScrollBarVisibility="Disabled" 
               Background="#FF2AB25B" />
        <DockPanel  Grid.Row="2" Margin="5">
            <Border CornerRadius="6" BorderBrush="Gray" BorderThickness="2" >
                <StackPanel Grid.Column="0" Grid.Row="2">
                    <!-- Nombre-->
                    <StackPanel Orientation="Horizontal" Margin="10" Width="372" >
                        <Label Content="Nombre:" FontSize="16" Foreground="Black" />
                        <TextBox  Width="250" Margin="50,0,0,0" IsReadOnly="true" Background="Beige"
                                  Text="{Binding Path = Nombre}" FontWeight="Bold" />
                    </StackPanel>
                    <!-- Fin Nombre-->
                    <!-- Commentario-->
                    <StackPanel Orientation="Horizontal" Margin="10" Width="372">
                        <Label Content="Comentario:" FontSize="16" Foreground="Black" Width="98"/>
                        <TextBox Width="244" Margin="30,0,20,0" 
                                 Text="{Binding Path = Comentario}" Background="Beige"/>
                    </StackPanel>
                    <!-- Fin Commentario-->
                    <!-- Marca-->
                    <StackPanel Orientation="Horizontal" Margin="10" Width="369">
                        <Label Content="Marca:" FontSize="16" Foreground="Black" Width="88"/>
                        <TextBox  Width="251" Margin="30,0,20,0" 
                                 Text="{Binding Path = Marca}" Background="Beige"/>
                    </StackPanel>
                    <!-- Fin Marca-->
                </StackPanel>
            </Border>
        </DockPanel>
        <Button x:Name="btnGuardar" 
                Content="GUARDAR" Grid.Row="3" 
                FontWeight="Black" Click="btnGuardar_Click" />
            
    </Grid>
</Window>
....