I recently had to output a personalized copy of a document to a few hundreds of users. Unfortunately, TCPDF cannot open/read an existing PDF nor can it use a PDF as template.
Fortunately, I stumbled on FPDI which extends TCPDF with this feature. It's pretty easy to implement so I won't go into the details.
TCPDF – http://www.tcpdf.org
FPDI - http://www.setasign.de/products/pdf-php-solutions/fpdi/demos/tcpdf-demo/
