Nginx: Make (PDF) file downloadable when accessed with parameter '?download=1'

default

# http://mysite.com/media/file.pdf
# absolute path: /path/to/media/directory/file.pdf
location /media {
  alias /path/to/media/directory;
  expires max;
  access_log off;
  location ~* \.(pdf)$ {
    if ($arg_download = 1){
      add_header Content-Disposition 'attachment;';
    }
  }
}