You can create custom fields that create QRCodes with a code like this
return $Actions->QRCode("Text to transform to qrcode");
Since you can also retrieve the field information in the custom fields you could as well transform the field text into a qrcode like this:
$value= $Retriever->GetValueById('5'); if($value!=null) return $Actions->QRCode($value->GetHTML()->ToText()); return '';
Transform 5 with the id of your field (that you can find in the form builder or pdf builder).