Every document carries proof it has not been changed.
Anyone who receives one can check it themselves, in seconds.
How anyone can check
Scan the mark on the document, or enter the code by hand. It confirms immediately whether the document matches exactly what was originally sent, or whether something changed.
Verified people, not just verified paper
Some things need more than a document. A qualification. A completed job. Someone standing behind a result. Those get their own kind of check too, including an independent person confirming it in person when it matters most.
What this protects you from
A changed invoice. A forged certificate. A completion claim nobody can actually confirm. This closes that gap plainly.