how to react on file save using rules module
You can use Entity Rules I believe for this.
From the module page:

Entity Rules provides a page for selecting and creating Rules components that will be executed when different operations happen to an Entity of a particular bundle. This provides an alternative method of triggering Rules. Instead of adding entity related events to Reaction Rules you are able to select which Rules will fire from the bundle management page.
Currently the operations supported are create, update, delete, validation and form access. You are also able to pass different arguments to the Rules per bundle.

In Drupal 7 the de facto module is typically file_entity used alongside the media module so if you are using those then the above should work but if you are not you may at least need the file_entity module.
I also noticed an issue in the Entity Rules issues page that listed a bug with file_entity but has been fixed in dev, so if the normal version does not work I would try the dev version to see if that works.
Hope that helps!