Read Only Files in BONITA BPM 7.0.2 Community version

Hi! I'm working with Bonita BPM Community version, 7.0.2.
I have two human tasks named: Selectora and Supervisor. And a document named "datosingreso" which I defined in the pool where both tasks are.
In the contract of the Selectora task I add "datos" type file and also add an operation where I link "datosingreso" with the file "datos".
The goal of the process is that the Selectora upload a file which should be seen by the Supervisor. In other words, "datosingreso" file should be an input for the human task Supervisor. And there I have the problem; I can't find the way in which I can design that thing.
I couldn't find material regarding files in de tutorial videos.
Thank you for your help!!!