Upload a file to Drupal server from an outside URL

drupal_upload_file.php

function upload_file($path) {
   // This is a PHP function to get a string representation of the image file.
   $image = file_get_contents($path); 
   
   // A stream wrapper path where you want this image to reside on your file system including the desired filename.
   $destination = 'public://path/to/store/this/image/name.jpg'; 
   
   $file = file_save_data($image, $destination, FILE_EXISTS_REPLACE);
   
   if (is_object($file)) { // if you get back a Drupal $file object, everything went as expected so make the status permenant
      $file->status = 1;
      $file = file_save($file);
   }
   
   return $file;
}