Hello BJR
You are talking about the Swiss Half Fare Card. It is not a pass; it is not valid for travel without further tickets yet entitles you to purchase them at a reduced fare, with a reduction up to 50%.
Yes, you can screenshot the QR code or show the tickets and the Swiss Half Fare Card as part of a PDF document.
Wifi is not needed to view the tickets in the SBB Mobile app. Once you purchased the tickets you can simply view them in the app. They will remain available even when offline. In addition, for each ticket a purchase confirmation e-mail is sent.
No matter the way how you store and present the tickets (SBB Mobile app, PDF, e-mail, or screenshot) to the ticket inspector, you must always show your physically available passport or ID card issued by your government to prove your ID. Physically means, paper copies of it or images on smartphones of it are not accepted.
Kind regards,
Roland