OnDoc/ADDemo/Form1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.DirectoryServices;
using System.DirectoryServices.Protocols;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Net;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;


namespace ADDemo
{
    public partial class Form1 : Form
    {
        string Username = "";
        string ADError = "";
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            DirectoryEntry de = new DirectoryEntry();
            Get_User("meyering", ref de);
        }

        public class UserData
        {
            public string Name { get; set; } = "";
            public string Department { get; set; } = "";
            public string Office { get; set; }

        }

        private void trylogin()
        {
            try
            {
                LdapConnection connection = new LdapConnection("ldap.fabrikam.com");
                NetworkCredential credential = new NetworkCredential("user", "password");
                connection.Credential = credential;
                connection.Bind();
                Console.WriteLine("logged in");
            }
            catch (LdapException lexc)
            {
                String error = lexc.ServerErrorMessage;
                Console.WriteLine(lexc);
            }
            catch (Exception exc)
            {
                Console.WriteLine(exc);
            }


            //---------------------------
            using (DirectoryEntry adsEntry = new DirectoryEntry(path, strAccountId, strPassword))
            {
                using (DirectorySearcher adsSearcher = new DirectorySearcher(adsEntry))
                {
                    //adsSearcher.Filter = "(&(objectClass=user)(objectCategory=person))";
                    adsSearcher.Filter = "(sAMAccountName=" + strAccountId + ")";

                    try
                    {
                        SearchResult adsSearchResult = adsSearcher.FindOne();
                        bSucceeded = true;

                        strAuthenticatedBy = "Active Directory";
                        strError = "User has been authenticated by Active Directory.";
                    }
                    catch (Exception ex)
                    {
                        // Failed to authenticate. Most likely it is caused by unknown user
                        // id or bad strPassword.
                        strError = ex.Message;
                    }
                    finally
                    {
                        adsEntry.Close();
                    }
                }
            }

        }
        private void getusera()
        {
            UserData user = new UserData();
            DirectoryEntry entry = new DirectoryEntry("LDAP://DC=mydomain,DC=local");
            using (DirectorySearcher ds = new DirectorySearcher(entry))
            {
                ds.Filter = "(SAMAccountName=" + "myusername" + ")";
                ds.PropertiesToLoad.Add("displayName");
                ds.PropertiesToLoad.Add("name");
                ds.PropertiesToLoad.Add("department");
                ds.PropertiesToLoad.Add("physicalDeliveryOfficeName");
                var result = ds.FindOne();
                if (result != null)
                {
                    try
                    {
                        user.Name = result.Properties["name"][0].ToString();
                        user.Department = result.Properties["department"][0].ToString();
                        user.Office = result.Properties["physicalDeliveryOfficeName"][0].ToString();
                    }
                    catch { }
                }
            }
        }
        public bool Get_User(string Userid, ref DirectoryEntry de)
        {
            var enTry = new DirectoryEntry("LDAP://db.debian.org/uid=meyering,ou=users,dc=debian,dc=org");
            // Dim enTry As DirectoryEntry = New DirectoryEntry("LDAP://db.debian.org/uid=abi,ou=users,dc=example,dc=com")

            var mySearcher = new DirectorySearcher(enTry);
            mySearcher.Filter = "(SAMAccountName=" + Userid + ")";
            foreach (System.DirectoryServices.SearchResult resEnt in mySearcher.FindAll())
            {
                try
                {
                    de = resEnt.GetDirectoryEntry();
                    Username = de.Properties["givenname"].ToString() + de.Properties["sn"].ToString();
                    ADError = "";
                    return true;
                }
                catch (Exception ex)
                {
                    this.Username = "";

                    this.ADError = ex.Message;
                    return false;
                }
            }
            return false;
        }

    }


}