How to load field value to custom form?
You can try using system_settings_form which is simple way of storing settings in Drupal..

function registration_pdf_form($form, &amp;$form_state) {
   $form['registration_body_twoside'] = array(
        '#type' =&gt; 'text_format',
        '#title' =&gt; t('Two-sided PDF'),
        '#default_value' =&gt; variable_get('registration_body_twoside', ''),
    );
    $form['registration_body_threeside'] = array(
        '#type' =&gt; 'text_format',
        '#title' =&gt; t('Three-sided PDF'),
        '#default_value' =&gt; variable_get('registration_body_threeside', ''),
    );
  return system_settings_form($form);
}


you can read values using

$twoside = variable_get('registration_body_twoside', '');
$threeside = variable_get('registration_body_threeside', '');