He seems to be using some kind of QR code API/service that he has registered as a service instance via the SmartObject Service Tester.exe found in K2’s bin folder. He ufortuanately does not show which QR code Api/service he used, nor how he did it. However the K2 barcode control maybe able to read 2D codes (such as QR codes):
Im not sure is this control is available in 4.7 or how it will read from a PDF, but it is available in K2 Five and it can be read from an image attachment control. I will attach the full k2 Barcode document.