Self Service - Document uploads

It would be great if customer can sign-up for a service and upload their personal documentation via the customer portal instead of uploading during the sign-up process.

The sign-up process normally takes place on a mobile device. Not a lot of tech savvy customers can upload documentation from their mobile phone but prefer to upload via PC. This can hold-up the process. With an upload documents later, the customer can complete sign-up and upload their documents on the portal at a later/more convenient time.

We require a way to upload (Not delete) documentation via customer portal as well as mobile customer app as part of self services