It's not difficult to find examples:

https://twitter.com/gruber/status/991122089557004288?lang=en

There is even whole industry around the concept, it is called trusted timestamping: https://en.wikipedia.org/wiki/Trusted_timestamping

It basically works like this, you compute a hash of the document and send to some kind of service that will either publish your hash with the timestamp or will also sign the hash and the timestamp cryptographically without ever touching the document.

Later, you can refer somebody to the external service or let them examine the signature and the hash to prove that you were in possession of the information before certain date and time.