Pauchueni44
Yes, anything “half fare” as reduction option in your personal details is fine for purchasing tickets which will be valid along with your Swiss Half Fare Card. Whether you have a valid SHFC will be ONLY checked while travelling during a ticket control, NOT while purchasing tickets in advance. In other words, the validity period of the SHFC is relevant for the travel dates, NOT for the ticket purchase dates.
The SHFC comes as e-Ticket = QR code, it doesn’t matter how you display it for the ticket inspector’s control device scanner. The confirmation e-mail or a saved PDF on your mobile are fine, a printout is not absolutely necessary (unless you’re often running out of phone battery).