How do I add a file upload button?
There is a beta version of a module that can help you achieve this:

https://www.drupal.org/project/views_entity_form_field 


  This module provides the ability to add form field widgets to a view to edit multiple entities at one time.
  
  Form field options will show up in a View's "Add field" list, prefixed with "Form field: " and then the name of the field being added.