Got the Date by inserting
public function insertDocumentCreditDate(Zend_Pdf_Page $page, $text)
{
$page->setFillColor(new Zend_Pdf_Color_GrayScale(0));
$this->_setFontRegular($page, 10);
$docHeader = $this->getDocHeaderCoordinates();
$page->drawText($text, 35, 547 - 10, 'UTF-8');
}
to Abstract.php
and then
$this->insertDocumentCreditDate(
$page,
Mage::helper('sales')->__('Created: ') . date( 'd.m.Y', strtotime($creditmemo->getCreatedAt()))
);
to Creditmemo.php