How to display the Alfresco Document on an Activiti form by passing its nodeRef to a form variable

[lazlondon]

Using the activiti-app (Kick Start), created a process.

There is a Referenced Form on the Start Event, with a field 'Attach File'.

How can I automatically upload an existing Alfresco Share document to this form when a third party application passing the nodeRef to the form using Activiti REST API? So the end result should be the same when someone manually upload existing Alfresco Share document on the form.