@Html.DropDownList("Contrat",new SituationMatrimonialeModel().ContratPacs.ToSelectList(), "", new { @class = "form-control", @id = "contractPacs", @onchange = "ContratPacs()", @for = "pp1P" })

public ContratPacs ContratPacs { get; set; }

public enum ContratPacs
    {
        [Display(Name = "Contrat Authentique")]
        ContratAuthentique = 1,

        [Display(Name = "Contrat Sous Seing Privé")]
        ContratSousSeingPrive = 2,

    }

HtmlHelper<MoiModel>' does not contain a definition for 'EnumDropDownListFor' and no extension method 'EnumDropDownListFor' accepting a first argument of type 'HtmlHelper<MoiModel>' could be found (are you missing a using directive or an assembly reference?)  

using System.Web.Mvc.Html.HtmlHelper

'HtmlHelper' does not exist in the namespace 'System.Web.Mvc.Html' (are you missing an assembly reference?)  

in una mia classe Utilities

 public static SelectList SelectListFor<T>()
        where T : struct
    {
        var t = typeof(T);

        if (!t.IsEnum)
        {
            return null;
        }

        var values = Enum.GetValues(typeof(T)).Cast<T>()
                       .Select(e => new { Id = Convert.ToInt32(e), Name = e.GetDescription() });

        return new SelectList(values, "Id", "Name");
    }

    public static string GetDescription<TEnum>(this TEnum value)
    {
            var field = value.GetType().GetField(value.ToString());
            DisplayAttribute[] displayAttributes = (DisplayAttribute[])field.GetCustomAttributes(typeof(DisplayAttribute), false);

            if (displayAttributes.Length > 0)
            {
                var elementAtOrDefault = displayAttributes.ElementAtOrDefault(0);
                if (elementAtOrDefault != null)
                    return elementAtOrDefault.Name;
            }
            return value.ToString();
        }

    }

  public enum ContratPacs
    {
        [Display(Name = "Contrat Authentique")]
        ContratAuthentique = 1,

        [Display(Name = "Contrat Sous Seing Privé")]
        ContratSousSeingPrive = 2,

    }

 @Html.DropDownListFor(client => client..ContratPacs, Utilities.SelectListFor<ContratPacs>(), "", new { @class = "form-control", @id = "contratPacs" })