Convert plain PDF to PDF/A-3b

pdfa_convert.php

<?php

use horstoeko\zugferd\ZugferdPdfWriter;

/**
 * Converts a plain PDF to PDF/A-3b (without attachments).
 * @param string $sourcePdf Source PDF file name
 * @param string $destPdf Destination PDF file name (can be the same as the source)
 * @param string $title Title metadata
 * @param string $author Author metadata
 * @param string $creatorTool Creator tool metadata
 * @return void
 */
function convert_pdf_to_pdfa(string $sourcePdf, string $destPdf, string $title, string $author, string $creatorTool=''): void
{
	$pdfWriter = new ZugferdPdfWriter();

	// Copy pages from the original PDF

	$pageCount = $pdfWriter->setSourceFile($sourcePdf);

	for ($pageNumber = 1; $pageNumber <= $pageCount; ++$pageNumber) {
		$pageContent = $pdfWriter->importPage($pageNumber, '/MediaBox');
		$pdfWriter->AddPage();
		$pdfWriter->useTemplate($pageContent, 0, 0, null, null, true);
	}

	// Set PDF version 1.7 according to PDF/A-3 ISO 32000-1

	$pdfWriter->setPdfVersion('1.7', true);

	// Update meta data (e.g. such as author, producer, title)

	$pdfMetadata = array(
		'author' => $author,
		'keywords' => '',
		'title' => $title,
		'subject' => '',
		'createdDate' => date('Y-m-d\TH:i:s') . '+00:00',
		'modifiedDate' => date('Y-m-d\TH:i:s') . '+00:00',
	);
	$pdfWriter->setPdfMetadataInfos($pdfMetadata);

	$xmp = simplexml_load_file(ZugferdSettings::getFullXmpMetaDataFilename());
	$descriptionNodes = $xmp->xpath('rdf:Description');

	// rdf:Description urn:factur-x:pdfa:CrossIndustryDocument:invoice:1p0#
	// $descriptionNodes[0] not applicable

	// Factur-X PDFA Extension Schema http://www.aiim.org/pdfa/ns/extension/
	// $descriptionNodes[1] not applicable

	// rdf:Description http://www.aiim.org/pdfa/ns/id/
	// PDF/A-3b declaration
	$descPdfAid = $descriptionNodes[2];
	$pdfWriter->addMetadataDescriptionNode($descPdfAid->asXML());

	// rdf:Description http://purl.org/dc/elements/1.1/
	$descDc = $descriptionNodes[3];
	$descNodes = $descDc->children('dc', true);
	$descNodes->title->children('rdf', true)->Alt->li = $pdfMetadata['title'];
	$descNodes->creator->children('rdf', true)->Seq->li = $pdfMetadata['author'];
	$descNodes->description->children('rdf', true)->Alt->li = $pdfMetadata['subject'];
	$pdfWriter->addMetadataDescriptionNode($descDc->asXML());

	// rdf:Description http://ns.adobe.com/pdf/1.3/
	$descAdobe = $descriptionNodes[4];
	$descAdobe->children('pdf', true)->{'Producer'} = 'FPDF';
	$pdfWriter->addMetadataDescriptionNode($descAdobe->asXML());

	// rdf:Description http://ns.adobe.com/xap/1.0/
	$descXmp = $descriptionNodes[5];
	$xmpNodes = $descXmp->children('xmp', true);
	$xmpNodes->{'CreatorTool'} = $creatorTool;
	$xmpNodes->{'CreateDate'} = $pdfMetadata['createdDate'];
	$xmpNodes->{'ModifyDate'} = $pdfMetadata['modifiedDate'];
	$pdfWriter->addMetadataDescriptionNode($descXmp->asXML());

	// Save file

	$pdfWriter->Output($destPdf, 'F');
}

Requires this library: https://github.com/horstoeko/zugferd/