Document Assembly, How?

[jenbrink]

Client is a law firm that whats to be able to have users fill out their own Wills, power of attorneys, etc.

He wants them to be able to pay for them first. Then fill in a form and when submitted, it assembles into a template to print or email.

I'm lost on this one. Can anyone recommend a software, or service that will be able to do both, shopping cart and document assembly?

Thanks for any help!