Im using [PDF Using MPDF](https://www.drupal.org/project/pdf_using_mpdf) module to generate 4 files when a node is saved using its API function `pdf_using_mpdf_api`:

```
function MYMODULE_node_insert($node){
        // PDF generation :
        // Generate standard version
        $view = node_view($node, 'PDF');
        $html = drupal_render($view);
        pdf_using_mpdf_api($html, 'reference_'.$node->nid);

        // Generate short version
        $view = node_view($node, 'pdf_short');
        $html = drupal_render($view);
        pdf_using_mpdf_api($html, 'reference_'.$node->nid.'_short');

        // Generate Standard EN version
        $view = node_view($node, 'pdf_en');
        $html = drupal_render($view);
        pdf_using_mpdf_api($html, 'reference_'.$node->nid.'_en');

        // Generate short EN version
        $view = node_view($node, 'pdf_short_en');
        $html = drupal_render($view);
        pdf_using_mpdf_api($html, 'reference_'.$node->nid.'_short_en');
}

```

this code above generates 4 pdf files correctly and save them under `default/files/pdf_using_mpdf` directory.
users should be able to download these PDFs, so I added 4 fields in my content type for each PDF version (field\_pdf1, field\_pdf2, field\_pdf3, field\_pdf4).

I want to attach these stored files into their corresponding fields inside private directory (after success, i'll remove them from default/files/pdf\_using\_mpdf directory).

Before Im used to use `field_attach_update` to attach fields to a node, but for file fields how can I do this ?

What should be the value of the field : `$node->field_pdf1['und'][0]['value']` ? and how can I store them into private directory ?

Thanks in advance.