But I personally like having paper that the corporation printed out versus something that I printed out. Like, technically, you can fake the "receipt" page because it's just some html etc. The only thing that proves that what you have is real is the confirmation number and suddenly you're back to hoping that the corporation that asserts you owe them money has and will provide all of their sql databases so that you can show that your confirmation number is genuine.
On the other hand, if I have years of documents they produced and the styles and layout, paper quality, postal records, etc all match what everyone else has in their homes, then, yeah, it could still be faked, but it's a much harder pill for a judge to swallow. Like, at some point people are going to decide that you're either telling the truth or you are a super genius with way too much time on your hands. Either way they're going to tend towards letting you off the hook.