In fact, I think the entire small-scale financial sector hasn't quite caught up to the fact that things simply aren't done on paper these days. If you download the P46 from the HMRC web site, it isn't a PDF form. It's just an image-only PDF. And what is the acceptable version of a receipt for a transaction which issued only an electronic one? A screenshot of the email/web page? Do I have to print it and scan it?
I neither own, nor wish to own, nor have space for a printer.