The Canadian passport application PDF has Javascript that updates a QR code in the top-right corner of the first page whenever you change or fill in a field.

https://www.canada.ca/content/dam/ircc/migration/ircc/englis...

Seems like a pretty genius way of avoiding transcription errors. When I dropped my passport application off yesterday the passport officer marked up a few things on the PDF and then scanned it in, so I assume that they use the QR code to automatically fill in the data as I entered it and then make any updates necessary from after-the-fact modifications manually.

Only seemed to work correctly in Acrobat Reader, but I haven't tried others (like Foxit) or anything.