Get a document id based on user input data

$doc = $modx->newObject('modResource');
$doc->set('class_key','modResource');
$doc->set('context_key','web');
$doc->set('type','document');
$doc->set('contentType','text/html');
$doc->set('pagetitle',$pagetitle);
$doc->set('longtitle',$longtitle);
$doc->set('introtext',$introtext);
$doc->set('alias',$alias);
$doc->set('published','1');
$doc->set('parent','34');
$doc->set('isfolder','0');
$doc->setContent($content);
$doc->set('richtext','1');
//$doc->set('menuindex','99');
$doc->set('searchable','1');
$doc->set('cacheable','1');
//$doc->set('menutitle','FAQ');
$doc->set('donthit','0');
$doc->set('hidemenu','0');
$doc->set('publishedon',$publishedon);
$doc->set('template',$template);
 
$doc->save();

// Save TVs for NEWS
$tv = $modx->getObject('modTemplateVar', array ('name'=>'mod')); 
$tv->setValue($doc->get('id'), $mod);
$tv->save();

$tv = $modx->getObject('modTemplateVar', array ('name'=>'tb_send_date')); 
$tv->setValue($doc->get('id'), $send_date);
$tv->save();

$doc = $modx->newObject('modResource');

<?php
        $response = $this->modx->runProcessor('resource/create', $fields);

        /* @var $response modProcessorResponse */
        if ($response->isError()) {
            if ($response->hasFieldErrors()) {
                $fieldErrors = $response->getAllErrors();
                $errorMessage = implode("\n", $fieldErrors);
            } else {
                $errorMessage = 'An error occurred: ' . $response->getMessage();
            }
            $this->setError($errorMessage);
            return '';

        }