Import files into a file field in Drupal 7
I am currently working on the exact same thing, except using photos.  If you click my profile name, you will see a series of questions related to learning how to do what you are asking to do.

I was able to easily accomplish the code to loop through all the files in my folder and add them to my nodes. 

$file = new stdClass();
$file-&gt;filename = basename($local_path);
$file-&gt;filepath = $local_path;
$file-&gt;uri = $local_path;
$file-&gt;filemime = $mime;
$file-&gt;filesize = filesize($local_path);

// Set this at the very beginning to correspond to USER you want posting items.
$file-&gt;uid = $uid; 
$file-&gt;status = FILE_STATUS_PERMANENT;
file_save($file);

$images[] = array(
'fid' =&gt; $file-&gt;fid,
'alt' =&gt; $page_data['title'],
'title' =&gt; $page_data['title']
);