On PHPBuilder.com today there's a new tutorial about creating editing PDFs with the help of the FPDF library.

Because the Web has become the primary mechanism for distributing PDF documents, it's common to encounter questions on various web development forums pertinent to the dynamic creation of PDF documents using languages such as PHP. [...] Thankfully, such a demand for PDF manipulation capabilities exists within the PHP community that numerous alternative open source solutions have long been available, including notably FPDF.

They help you get the library installed and show you how to create a basic PDF with some simple text inside. They build on this and show how to add multiple text sections, images and watermarks.