PDF/A exsiting pdf with TCPDF and FPDI - php

Question

Hello my task is to certify pdf with digital Signature Certification and release it in pdf/a format. I tried using tcpdf, but i couldn't import existing pages. So I added fpdi, kind of mixing them:
require_once('./tcpdf/tcpdf.php');
require_once('./tcpdf/fpdi.php');
$pdf = new FPDI( );
//$pdf = new TCPDF(PDF_PAGE_ORIENTATION, PDF_UNIT, PDF_PAGE_FORMAT, true, 'UTF-8', false, true);
$file = realpath("484.pdf");
$pagecount = $pdf->setSourceFile($file);
for($i = 1 ; $i <= $pagecount ; $i++){
$tpl = $pdf->importPage($i);
$size = $pdf->getTemplateSize($tpl);
$orientation = $size['h'] > $size['w'] ? 'P':'L';
$pdf->AddPage($orientation);
$pdf->useTemplate($tpl, null, null, $size['w'], $size['h'], true);
}
$pdf->SetCreator("Creator");
$pdf->SetTitle('123Titel');
$pdf->SetDefaultMonospacedFont(PDF_FONT_MONOSPACED);
$certificate = 'file://123.crt';
$info = array(
'Name' => '123test',
'Location' => 'place',
'Reason' => '123',
'ContactInfo' => '123',
);
$pdf->setSignature($certificate, $certificate, '123', '', 2, $info);
$pdf->SetFont('helvetica', '', 12);
$pdf->addEmptySignatureAppearance(0, 0, 0, 0);
$pdf->Output('test.pdf', 'F');
Alright, so I can put signature in alright with this, but i cant make it pdf/a.
What decides pdf/a format is
$pdf = new TCPDF(PDF_PAGE_ORIENTATION, PDF_UNIT, PDF_PAGE_FORMAT, true, 'UTF-8', false, true);
The last "true". But I cant use this tcpdf function, or i get:
Call to undefined method TCPDF::setSourceFile() in...
So im forced to use $pdf = new FPDI( );, which can't save pdf in pdf/a format
Surely someone knows something that im missing and im running out of ideas on what to do.
-Can I import existing pdf with only tcpdf and if yes HOW?
-Is there any other way to make file format pdf/a (i coudlnt find any)
-Any tips whatsoever

Answer 1

It appears that I can extend tcpdf with fpdi. Somehow it didnt work until i changed fpdi_bridge to always extend tcpdf and changed
new FPDI();
to
new FPDI(PDF_PAGE_ORIENTATION, PDF_UNIT, PDF_PAGE_FORMAT, true, 'UTF-8', false, true);