Reading AD Pagewise

        public IEnumerable<UserAccount> GetPage(string sortField, int start, int Number)
        {
            UserPrincipalEx findAllUsers = new UserPrincipalEx(thisOU);
            PrincipalSearcher ps = new PrincipalSearcher(findAllUsers);
            ((DirectorySearcher) ps.GetUnderlyingSearcher()).PageSize = 0;
            ((DirectorySearcher)ps.GetUnderlyingSearcher()).Sort = new SortOption("cn", SortDirection.Ascending);
            ((DirectorySearcher)ps.GetUnderlyingSearcher()).VirtualListView = new DirectoryVirtualListView(0, Number, start);
            PrincipalSearchResult<Principal> result = ps.FindAll();
            foreach (UserPrincipalEx user in result)
            {
                string firstName = user.GivenName;
                string lastName = user.Surname;
                string orgKennzeichen = user.ExtensionAttribute8;
                string samAccountName = user.SamAccountName;
                UserAccount _user = new UserAccount()
                {
                    FirstName = firstName,
                    LastName = lastName,
                    OrgKennzeichen = orgKennzeichen,
                    SAMAccountName = samAccountName
                };
                yield return _user;
            }
        }