By default and for security reasons, users a re allowed to upload only certain types of extensions which are safe and secure.

HJowever, clinets might need other extensions to be regognized by the module. Therefore there are some changes in the core to be done

1. uploadify/uploadify.php, Line 28
    $file_types = array('jpg', 'jpeg', 'gif', 'png', 'youextension'); /* File extensions */

2. controllers/admin/AdminDigitalFiles.php, line 22
    public $file_extensions = array(
        'jpg', 'jpeg', 'gif', 'png', 'pdf', 'epub', 'zip', 'youextension'
    );


Please note that the module cannot be updated as a result of the changes. If you want to update the module, the changes will be overwritten. You will have to apply them again in the hope that they will still be compatible with the new version.