C # search the Office field in LDAP

Good afternoon, I need a great help, I have a DAP access authentication, it is working correctly, validating username and password. However, I need a DAP field returned, this field is the "office", where we store information about the user's enrollment. It is critical that this field be (Office). Thank you in advance.

using System;

using System.Collections.Generic;

using System.Text;

using System.Data.SqlClient;

using System.Data;

using System.DirectoryServices;
using System.Web;

namespace ActiveDirectory

{

    public class AuthoAD

    {

        public string Autentica(string User, string Senha)

        {

            string retorno = string.Empty;

            try

            {

                DirectoryEntry objAD = new DirectoryEntry("LDAP://master.meudominio.local:389", User, Senha);


                HttpContext.Current.Session["login"] = objAD.Name;

                retorno = objAD.Name;

            }

            catch (Exception ex)

            {
                HttpContext.Current.Session["login"] = "";
                throw new Exception(ex.Message);
            }
            return retorno;

        }

    }

}