我的PHP页面（或表单）自动解码html实体

I have a problem with my form that send variables to a page that have TCPDF to print values:

if I write this directly inside my textarea:

<p>&lt;TEST</p>

and click submit, my destination page, using var_dump show me:

<p><TEST</p>

That result BREAK my TCPDF building!

Why result are automatically decoded? How to prevent this?

My destination page:

<?php

$text = $_POST['testo'];

header('Content-Type: text/html; charset=utf-8');

$pdf = new MYPDF(PDF_PAGE_ORIENTATION, PDF_UNIT, PDF_PAGE_FORMAT, true, 'UTF-8', false);

$pdf->SetFont('dejavusans', '', 8, '', true);

$pdf->AddPage();

$pdf->writeHTML($text, true, false, true, false, '');