They shouldn’t have to actively verify that, but yeah, I don’t know if there is a relevant file format though

I once worked with signed xml, where the signature field is really no different than any other field, but with binary data. That data used a private key to sign a checksum if the file. For tools that understand the format, you just verify the trust chain against cert authority public keys using your local keystore. It just worked, with no action required of the user and no internet required

• if you edit the signature, the trust chain will fail validation
• if you edit other data, the signed checksum would not match and validation would fail
• if you edit the checksum, the key would no longer match and validation would fail

It’s actually been a lot of years, so I hope I’m remembering it accurately