You need two things from whoever sent you the documents:
the certificate or proof file (it ends in .json), and
the documents to check, exactly as you received them.
Drop them all in below. The check happens on your own computer: nothing is uploaded.
Drop the certificate and documents here, or
Green
The document is unchanged since the time shown, and both independent proofs of that time check out.
Amber
The document is unchanged and its signed time is valid; the Bitcoin proof is still pending or could not be reached.
Red
Do not rely on it: the document has been changed, is not on the certificate, or a proof failed. The reason is given.
Advanced: check it yourself, or use another Bitcoin explorer
This page reads the public Bitcoin blockchain through a block explorer; that is its only network request. You can point it at another one, or at your own node.
This page also works saved to your computer and opened from there, with no connection to Graticus.