Say for example I wanted to load an already existing PDF file, and then transpose text on top of that PDF file and save it again as a new PDF file. Essentially merging the two, with one being transposed on the other.
I don't want the PDF acting as the background to become an image as to lose quality, so that everything retains it's original vectored format.
How would I go about doing this merge?
I don't want to use software, maybe there's a script that does this?
dompdf itself is unable to perform this kind of action. You would need to generate your PDF documents independently then use a third-party library to merge the two documents.
Since you're using dompdf I'm guessing you might be looking for a PHP-based solution. Take a look at FPDI. After generating your PDF documents with dompdf you could then use FPDI to combine them.
I think this will work, but I haven't tested it:
<?php
// generate pdf documents
require_once('dompdf/autoload.inc.php');
$dompdf = new Dompdf();
$dompdf->loadHtml('<p>Hello</p>');
$dompdf->render();
file_put_contents('doc1.pdf', $dompdf->output());
unset($dompdf);
$dompdf = new Dompdf();
$dompdf->loadHtml('<p> </p><p>Hello</p>');
$dompdf->render();
file_put_contents('doc2.pdf', $dompdf->output());
// combine pdf documents
require_once('fpdf.php');
require_once('fpdi.php');
// initiate FPDI
$pdf = new FPDI('L');
// add a page
$pdf->AddPage();
// set the source file to doc1.pdf and import a page
$pdf->setSourceFile("doc1.pdf");
$tplIdx = $pdf->importPage(1);
// use the imported page and place it at point 10,10 with a width of 210 mm
$pdf->useTemplate($tplIdx, 10, 10, 210);
// set the source file to doc2.pdf and import a page
$pdf->setSourceFile("doc2.pdf");
$tplIdx = $pdf->importPage(1);
// use the imported page and place it at point 100,10 with a width of 210 mm
$pdf->useTemplate($tplIdx, 100, 10, 210);
$pdf->Output();