Fit existing small PDF to A4 with PDFLib

convert.php

<?php
$outfile = "";

$p = new PDFLib();

if ($p->begin_document($outfile, "") == 0)
	throw new Exception("Error: " . $p->get_errmsg());

$indoc = $p->open_pdi_document('label.pdf','');
if ($indoc == 0)
	throw new Exception("Error: " . $p->get_errmsg($p));

$page = $p->open_pdi_page($indoc, 1, "");
/* Start an A4 output page (210mm x 297mm) */
$p->begin_page_ext(842, 595, "");
/* Place the imported page without any scaling */
$p->fit_pdi_page($page, 0, 0, "boxsize={842 595} fitmethod=meet");
$p->end_page_ext("");
$p->close_pdi_page($page);

$p->end_document("");

$buf = $p->get_buffer();
$len = strlen($buf);

file_put_contents('out.pdf', $buf);cd
$p = 0;