Independent digital certification for each document. The precise prerequisites are depending on the authority asking for them. https://www.evernote.com/shard/s485/sh/2b3977db-c11d-9758-e891-f0148286f375/WOpKaFgH9hzvemax6h-OENAzxb2o43R6rFL9QOXeuTngaLt_hinlEUJMdQ