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The short answer
To prove a document existed on a certain date, you need a record made at that time, held outside your own control, and tied to the document's exact content. Two things have to be fixed together. The what is the content, usually as a SHA-256 hash: a fingerprint that changes if one byte of the file changes. The when is a time recorded by someone other than the person who benefits from the date.
Get both and you can show that this exact file existed no later than that moment. Notice how narrow that claim is. It does not show the file was first written then, who wrote it, or that what it says is true. For most disputes about which version existed when, that narrow claim is the one that matters.
Why the file's own dates are not enough
The dates you see in a file come from the file or from your computer, and neither is independent. A PDF's Created and Modified dates are editable text. A file's date on disk changes when it is copied or restored, and follows whatever the computer's clock says. An email's date shows when a message was sent from that account, and the copy in your own mailbox is under your control.
These can still be useful, especially when several of them agree and an outside system holds a matching copy. They are weak on their own because the person relying on them is often the same person who could have changed them.
The options compared
Each method proves something slightly different, so choose by who will have to accept the proof. If a date could matter in a legal dispute, ask counsel which method they would want to rely on before you need it.
| Method | What it shows | Where it falls short |
|---|---|---|
| Emailing it to yourself | A message passed through a mail server on that date | You control the mailbox, and a colleague's copy depends on their mailbox being kept |
| Posting it to yourself | An envelope was postmarked on that date | Says little about what was inside when it was sealed, and nothing about a digital file |
| Notary | A person checked an identity or witnessed a signature on that date | Records a person's act on paper. Most notarizations are not a test of a digital file's exact bytes |
| Trusted timestamp (RFC 3161) | A timestamp authority signed the file's hash and a time | You must keep the token and the exact file, and need software that can check it |
| Qualified timestamp (eIDAS) | The same, from a qualified EU provider. EU law presumes its time and integrity accurate | The presumption applies under EU rules, and each stamp comes from a qualified provider |
| Blockchain anchor | The hash was included in a public chain by a certain block | Outside readers often need the method explained, and you must keep the proof data |
| Signed ledger record (Document Anchor) | An organization's key signed the hash, and the ledger recorded the time | The time comes from the ledger's operator, not an independent timestamp authority |
How to do it
1. Finish the document. Make the file final first, because the proof covers these exact bytes and nothing else. If you will send a PDF, record the PDF, not the Word file it came from.
2. Fingerprint it. The hash can be made on your own computer, so the content never has to leave it. The commands below work on a standard install.
3. Record the fingerprint with someone outside. A timestamp authority, a public chain or a signed ledger all do this. Do it now, not when a dispute starts, because the record is only worth anything if it was made at the time.
4. Keep the exact file. Opening a PDF and saving it again can change its bytes, and then it will no longer match, even if it looks identical. In our test, a clean re-save of a one-page PDF changed its hash. Keep the original somewhere it will not be touched.
5. Check it once. Hash the stored copy and confirm it matches the record. It is better to find a problem today than in the middle of a dispute.
# Mac or Linux
shasum -a 256 contract-signed.pdf
# Windows PowerShell
Get-FileHash contract-signed.pdf
What Invoance records, and how anyone checks it
Document Anchor is the signed ledger row in that table. Drop a file in the Invoance dashboard, or send its hash from your own code or through the Claude or ChatGPT connector. Your browser or code computes the SHA-256, and only the hash is sent unless you choose to store the original. Invoance signs the hash with your organization's Ed25519 key and records the time in an append-only ledger.
Each record gets a public proof page. Anyone holding a copy can drop it there and see match or no match, with no account and nothing uploaded. The page also shows which organization issued the record and whether that organization's domain is verified. A record that passes your plan's retention period is sealed from list views but still verifies.
The record is designed to be useful to someone who is not technical and does not trust you, which is the usual situation when a date is questioned. It is not a qualified timestamp, and Invoance is not a timestamp authority. The time comes from Invoance's ledger, so where you need the EU presumption of accuracy, use a qualified provider, alongside this record if a public check would also help.
Anchor once, verify any time
Invoice #1042Anchor 22 June 2026, the moment the invoice is issued
- Final fileinvoice-1042.pdfIssued to the customer
- SHA-256a94a8fe5…6b81Hashed on your side
- POST/v1/document/anchorOnly the hash is sent
- Signed record2026-06-22 14:09:51ZEd25519 · append-only ledger
Verify any day after, by anyone holding a copy
- Copy in handinvoice-1042.pdfSent, forwarded, or attached
- SHA-256Re-hash the bytesIn the browser or your code
- CompareWith the recordHash, time and issuer
- Matcha94a8fe5…6b81The copy is the file you issuedNo match7c19d2e0…a3f4Total edited from 4,200 to 42,000
What this proof does not show
A match shows this exact file existed by the recorded time. It does not show the file was created then, because it may be older. It does not show who wrote it, or that its contents are true: a false statement that gets recorded is still false, with a date on it. It says nothing about a document that was never recorded.
It also cannot be added afterwards. You can record a file today, but that only proves it existed today. Whether a record helps in a particular dispute depends on the rules and the people involved, so treat this as evidence for someone to weigh, not as a guarantee.
When to record a document
Record a document at the moment its date would matter later. In practice that means contracts when they are signed, invoices and payment instructions when they are issued, reports and filings when they are submitted, board minutes and policies when they are approved, and designs or research notes when you want to show what you had by a certain day.
Pick the one document your team is most likely to argue about and start there. If the argument is about what you sent, not only when it existed, the record works better when it goes out with the document. Put the proof link in the email, and whoever receives the file can check it without asking you.