<form action="" method="post">
   <div class="input_field">
        <input type="submit" value="Get Data" class="btn waves-effect waves-light myBlue" name="get_data">
    </div>
</form>

<?php

$user = checkConnected($bdd)
checkAutorisation($user, true);



if (!isset($_POST['get_data'])) {

    $pdf = new FPDF('P', 'mm', 'A4');
    $pdf->SetFont('Arial', 'B', 16);
    $pdf->Cell(40, 10, 'Hello World !', 1);
    $pdf->Output();
}

require('views/Head.php');
require $_dir["front"] . "file.php";

use FpdfFpdf;