<select name="titel" id="titel" value="">
    <option value="">Selecteer</option>
    <?php
    if($rowCount > 0){
        while($row = $query->fetch_assoc()){
            echo '<option  value="'.$row['titel'].'">'.$row['titel'].'</option>';
        }
    }else{
        echo '<option value="">Language not available</option>';
    }
    ?>
 </select>

2nd page (search.php):

<?php
//load database connection
$host = "localhost";
$user = "...";
$password = "...";
$database_name = "...";
$pdo = new PDO("mysql:host=$host;dbname=$database_name", $user,  $password, array(
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
));
// Search from MySQL database table

$titel=$_POST['titel'];
$version=$_POST['version'];

$query = $pdo->prepare("SELECT DISTINCT * FROM Library  where titel = ?  AND version = ?");

$query->bindValue(1, $titel, PDO::PARAM_STR);
$query->bindValue(2, $version, PDO::PARAM_STR);
$query->execute();