HTML returning a PDF?

Heya all --

I have a client who is requesting an HTML form that updates a database, then returns a PDF that includes some of the data entered in the form. The PDF is an existing document, and is quite extensive, so creating a new one every time seems inefficient. I'd love to be able to put some input fields on the PDF, and have a server-side script propigate the fields with the incoming data, then flatten the PDF and return it. Does anyone know if this is possible, and if so how would it be done?

Thanks so much for any help!

-Lucas