Blatant self promotion: Try my php-pdftk package. If you have pdftk
installed, it's very easy to use.
composer require mikehaertl/php-pdftk
<?php
use mikehaertl/pdftk/Pdf;
$pdf = new Pdf('form.pdf');
// Fill in UTF-8 compliant form data!
$pdf->fillForm(array('name' => 'Any char: ÄÖÜ'))
->saveAs('filled.pdf');
// Alternatively: Send to browser for download...
$pdf->send('filled.pdf');
// ... or inline display
$pdf->send();