using System.Windows.Forms;
using System.DirectoryServices.AccountManagement;

namespace WindowsFormsApplicationAD
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        readonly static string sDomain = "msk.mts.ru";
        readonly static string sDefaultRootOU = "DC=msk.mts,DC=ru";
        readonly static string sServiceUser = "*********";
        readonly static string sServicePassword = "***********";

        public static PrincipalContext GetPrincipalContext()
        {
            return new PrincipalContext(ContextType.Domain, sDomain, sDefaultRootOU, sServiceUser, sServicePassword);
        }

        public static UserPrincipal GetUser(string sUserName)
        {
            PrincipalContext oPrincipalContext = GetPrincipalContext();
            return UserPrincipal.FindByIdentity(oPrincipalContext, IdentityType.SamAccountName, sUserName);
        }


        private void button1_Click_1(object sender, EventArgs e)
        {
            UserPrincipal UP = GetUser("aasorok8");
            MessageBox.Show(UP.DisplayName);
        }
    }
}

new PrincipalContext(ContextType.Domain)