I'm looking to sell custom-generated documents based on user input, and I'm looking for some pointers which tool or platform I might work with. This means:

1. The user will enter data into a form (some completely flexible, some choices from pre-defined options).
   
2. The user pays.
   
3. The user gets to download the document (or receives it via email).

This whole journey might typically take between 1 and 15 minutes depending on the user.

The website in its current state is custom PHP, i.e. no Wordpress, and I don't want to switch to a new CMS if I can avoid it.

Ideally, I'd want a tool that covers all of the above, i.e.

1. can create the document itself based on input it receives via HTTP, meaning, I want to avoid embedding a form with bloat etc.,
   
2. handle the payment and then
   
3. supply the document to the user somehow.

Alternatively, I'd be fine with a payment solution that then redirects the user to a URL. In this scenario I guess my existing PHP setup would have to create a document on the fly and get confirmation from the payment provider to then supply the link to the user. (The obvious question here is how I can securely submit the URL to the tool without disclosing it to the user in the code somehow.)

The user input will likely contain personal data so privacy is a consideration.

Does anyone have experience with a similar process and can recommend anything?

Thanks!