> In the real world, documents and invoices in business are overwhelmingly sent in PDF format
This is evasive and dismissive. When your parent is talking about the issue, there's a good chance he is already using it. Telling him what "the real world" does is irrelevant. He has a use case already, and needs a solution for his use case, not for the rest of the world.
Almost every time on HN that there is a discussion of changes in technology that experts would argue are overall good, there is always someone who says “But that would break my use case!” This even got lampooned at xkcd[0]. OK, I understand that he finds this trend vexing. But no party to this discussion is obliged to spend their time and effort on suggesting a solution, especially when we don’t know his specifics and our suggestion might simply be rejected out of hand.
Except when it comes to GnuPG, you have to realize:
1. Many, many people used it, and continue to do so.
2. The anti GnuPG crowd keeps coming and touting alternatives, and then complain when the people in the prior bullet point out the impracticality of the alternatives for their use case.
We get that GnuPG has issues. We get that sometimes the alternatives are better. We can coexist with them. People simply don't understand that for a number of tasks, GnuPG is totally appropriate, and solves the problem with little pain.
This is evasive and dismissive. When your parent is talking about the issue, there's a good chance he is already using it. Telling him what "the real world" does is irrelevant. He has a use case already, and needs a solution for his use case, not for the rest of the world.