This addon lets you set the documents that need to be supplied by the client before the order can move forward.
You can set:
Now, when the client orders that product they will get an E-mail with the request to upload to a unique and obfuscated link.
Once they are uploaded, the client can go to a special page in the client area to see the status of the documents.
This while on the admin side you can check the documents and either approve or decline (with reason and request to upload again).