If you want to protect the date you wrote or changed documents,
or your stories, scripts, ideas, pictures, etc, print a copy and
send it to yourself through the mail. When you receive it back,
leave the envelope sealed, because the sorting office stamp mark
proves the date. You can also send it certified or return
receipt to have additional proof. Also handy if you cannot get a
witness, or get to the lawyer or business quickly. If it is very
sensitive, you can put the sealed envelope in your safe deposit
box.
With an email, you can
send it to yourself and not open it. The cloud will maintain
dates. Do the same with a file attachment for a quick free
backup.