Offers a convenient access to a single PDF document and its QR code like e.g. an EU Digital COVID Certificate. Unofficial app that is fully open source. This app is basically a super simple PDF reader with convenient fullscreen QR code rendering (if present in the PDF's 1. page). With more than 50000 downloads and for a while being one of the top 3 apps of Austria, this is my most succesful privately developed app so far.