I am looking for a service or tutorial that instructs on how to use the timestamping feature of the blockchain to record the existence and immutability of important documents.

We want to timestamp a document into the blockchain for a "proof of existence". It is also useful that the block will demonstrate the time it was created.

Does anyone on this board have a recommendation about which service to use or how to do this? It is preferable not to use a 3rd party.