Add widget to file field
You can check the hook_field_widget_info() 

function hook_field_widget_info() {
  return array(
    'text_textfield' =&gt; array(
      'label' =&gt; t('Text field'),
      'field types' =&gt; array('text'),
      'settings' =&gt; array('size' =&gt; 60),
      'behaviors' =&gt; array(
        'multiple values' =&gt; FIELD_BEHAVIOR_DEFAULT,
        'default value' =&gt; FIELD_BEHAVIOR_DEFAULT,
      ),
    );

}