FileDataExtension.php

<?php

/**
 * Class FileDataExtension
 */
class FileDataExtension extends DataExtension
{

    /**
     * @param FieldList $fields
     */
    public function updateCMSFields(FieldList $fields)
    {
        if (Permission::check('ADMIN')) {
            $fields->push(CheckboxField::create('ShowInSearch')->setTitle('Show In Search'));
        }
    }

    /**
     *
     */
    public function onBeforeWrite()
    {
        parent::onBeforeWrite();

        $this->owner->ShowInSearch = false;
    }

}