Hello Antonio,
If you refer your image above, "Add Documents" is an Action linked to a Project. So, if you refer the screenshot shown below, within the Actions tab, you can lookup the ID for the "Add Documents" action and then add it to the link here after action: http://*claritywebsite*/niku/nu#action:.... You should then be able to see the "Documents Manager" page on the UI.
In order to make changes to this Action link, try searching it within Admin -> Studio -> Views and it will directly take you to the link where the Views of the Document Manager will be saved, and you can then be able to configure the attributes. You can search it with the Object Name too i.e. Project.
Let me know if this is helpful.
Suhail.