How do I add a watermark to a PDF using PHP and without removing dynamic content?
<p>Recently I've been assigned to a project that requires adding a watermark to every page of a PDF file. However, while the PDF is always the same, the watermark for the PDF has to be custom-made to contain the email of any user who downloads it.</p>

<p>After some digging, I found the FPDF and <a href="https://www.setasign.com/products/fpdi/about/" rel="nofollow">FPDI</a> libraries for PHP. These libraries allow me to easily add custom watermarks to my PDF files, but by design they cause the resulting PDFs to lack Dynamic Content. The original PDF is quite large, so it requires internal links for easy navigation. Because PDFs edited with FPDI lacks dynamic content, those internal links are removed in the watermarked version of the PDF.</p>

<p>After some more searching, I've found an existing <a href="https://gist.github.com/andreyvit/2020422" rel="nofollow">workaround</a> for this problem using an extension of the FPDI library. However, that solution requires a vastly outdated version of FPDI that doesn't seem to function properly on my site.</p>

<p>All that said, my question is this: 
Barring the above solution, are there any existing PHP libraries that allow me to add custom watermarks to a pdf file without removing the original PDF file's internal links? I'm willing to pay for a license if I have to, but was hoping for a solution priced, at the very least, under $50.</p>