After drupal 6> 7 upgrade attached pdf links not visible After upgrade fromn 6 > 7  attachment information is not visible in nodes.  Data exists in dbase.  What is best approach to re-connecting pdf, mp3 and other attachments to specific nodes. (2000 or so)
Use CCK migrate module to migrate (import) the D6 fields to D7 . CCK migrate module is the part of CCK module in drupal 7.

Here is the documentation how to do it.