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).

To display information created from another plugin you can use custom fields located in the main menu of the plugin (This feature is only available in the full version)

Then define a custom field name, in which form this custom field is going to be used and the code of your custom field

The actual code that you need ...