Download file after login
Private files download permission


  Version 1.x provided "two useful features which Drupal itself is
  missing: a simple permission to allow downloading of private files by
  role, plus the ability to combine both public and private downloads".
  
  Version 2.x removes the "global" permission and implements a
  per-directory by-user and by-role filter instead, to let the
  administrator better tweak the whole website and increment the overall
  security.


with this module you can achieve your requirement by following this tutorial source

Hope it helps you!