download_file.module

<?php

// Link to /download_file/$fid to force download rather than view in browser

/*
* Implements hook_menu()
*/
function download_file_menu(){
  $items = array();
  $items['download_file/%'] = array(
    'title' => 'Download files',
    'description' => 'Description',
    'page callback' => 'download_file_view',
    'page arguments' => array(1),
    'access callback' => TRUE, // or 'check_access'
    'type' => MENU_CALLBACK
  );
  return $items;
}

function download_file_view($fid){
  $file = file_load($fid);
  if(isset($file->uri)){
    $url = file_create_url($file->uri);
    
    header('Content-Type: application/octet-stream');
    header("Content-Transfer-Encoding: Binary"); 
    header("Content-disposition: attachment; filename=\"".$file->filename."\""); 
    readfile($url);
  }else{
    drupal_not_found();
  }
  
  exit;
}

function check_access(){
  global $user;
  return $user->uid > 0;
}