Zend Framework features a really cool component called Zend_Pdf; its development is led by Alexander Veremyev.
We are currently trying to better understand the use-cases around how PHP developers are using Pdf files on the Web in order to figure out what the requirements are for future enhancements to our Pdf component.
Are you reading pre-formatted templates for invoices and just filling them in? Are you password protecting files depending on who downloads them?
Also, if there are just some discrete features you'd like to see please let us know too.
Please send feedback to the fw-formats mailing list. Even if you're currently not using Zend Framework we'd be very interested to hear about your use-cases. Thanks!