====== FPDF ======
http://www.fpdf.org/

FPDF is a PHP class which allows to generate PDF files with pure PHP, that is to say without using the PDFlib library.
====== FPDI ======
http://www.setasign.de/products/pdf-php-solutions/fpdi/

FPDI is a collection of PHP classes facilitating developers to read pages from existing PDF documents and use them as templates in FPDF, which was developed by Olivier Plathey.