I like this 

 In the same way PGP works? 

 yep, but with a social network of trusted keys you already know behind it 

 yeah, nostr makes a large, and usable WoT actually possible 

 "tweet on X" sounds like a gay sex thing. 

But I do think it would be helpful to have a way to sign documents with my nostr key (on mobile).

I'm a certified welding inspector. Part of my job description is certifying welders. There are currently no easy solutions to sign a PDF from my phone that don't involve paying a third party but more importantly becoming beholden to that third party to maintain the certifications that I issue. 

 We also could resolve the issues of PGP's unknown fingerprint.. verifying that a signature belongs to that npub.. 🎩💜
 nostr:nevent1qqsv452qgh9hn9gyp68vx4m47eswc4ht64rsv96cq9dxndk3upwuqsqpzamhxue69uhhyetvv9ujuurjd9kkzmpwdejhgtczyprqcf0xst760qet2tglytfay2e3wmvh9asdehpjztkceyh0s5r9cqcyqqqqqqgcnjmrh 

 This would enable us to cryptographically sign our communications beyond Nostr. I like it