Not a certified copy
It does not attest that the document is a true copy of an original, nor does it attest your identity. That is what a notary or the relevant authority does.
Certify a document online
Put on record that this document existed like this, today.
A contract, a quote, a report or any PDF: Sellat identifies the exact version and the date you protected it, and gives you a certificate anyone can check without relying on us.
Certify a document
We take you to the tool: you choose the file and receive the certificate by email.
Certificate and package A PDF certificate and a ZIP with the file and its verification data.
Public anchor The fingerprint is anchored in Polygon and in Bitcoin through OpenTimestamps.
Optional qualified timestamp You can add a qualified timestamp from the FNMT-RCM for €6.
What certifying means here
Two things it is not, and one it is.
“Certify a document” means very different things to different people. This is what Sellat does, said before you spend any time on it.
Not an electronic signature
It does not say who signed it or who agrees with its content. Signing and dating are different things, and this is the second one.
Proof of date and integrity
It records that this exact content existed on this date, and lets anyone check later whether the file is still the same, byte for byte.
Inside the package
This is exactly what you open two years later.
Not a promise and not a screenshot: the real list of files Sellat puts in your ZIP. What you see here is generated by the same module that builds the package.
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original/<archivo>If the original is keptYour file, byte for byte
The exact photo you sealed, in a folder of its own so no other file in the package can be mistaken for it. It travels inside when the original is available: the upload that created the proof, or custody.
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certificado-<id>.pdfAlwaysThe readable certificate
The PDF you show a person or attach to a filing. It is an informative document: what actually gets checked is the file, not the PDF. If the file carried Content Credentials (C2PA), the certificate records them too — who signed, with which tool and whether they declare AI use — exactly as your browser read them when you protected it.
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proof.jsonOnce the batch is anchoredThe portable proof
Your file fingerprint, its Merkle leaf and inclusion path, the batch root and the public transaction that records it. This is the piece that lets anyone check everything without Sellat.
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sello-cualificado-<id>.tsrWith a qualified sealThe qualified seal
The RFC 3161 response from the qualified timestamping authority, exactly as it was issued. This is the file that fixes the date under eIDAS.
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autoridad-sellado.pemWith a qualified sealWho signed the seal
That authority signing certificate, with its SHA-256 written into the README. It travels inside so the check works offline and nobody has to go looking for it.
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anclaje-bitcoin.otsOnce the batch is anchoredThe Bitcoin anchor
The OpenTimestamps proof of the batch root. It may still be waiting for a block: it is a valid file and whoever receives it can upgrade it themselves.
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LEEME.txt / README.txtAlwaysThe instructions, in two languages
What each file is, what it proves and what it does not, and the exact commands to check it. In Spanish and English, so an expert or a lawyer never has to ask you anything.
It checks out without us and without the internet.
With the seal and the authority certificate inside the ZIP, the date is verified with standard tools on the machine of whoever receives it. If Sellat disappeared tomorrow, your package would still check out.
The package proves that this exact file existed on that date and has not been modified. It does not prove who created it, who took the photo, or what happened in front of the camera.
How it works
From the file to the certificate, in three steps.
Nothing to install, and no blockchain to understand.
- 01
Choose the document
The exact version you want to be able to recognise later: the PDF you are about to send, not a copy re-exported afterwards.
- 02
Sellat creates the proof
It computes the SHA-256 fingerprint, records it and anchors it in public networks. You receive the certificate and the verification package by email.
- 03
Check it whenever you need to
Anyone can verify whether a file matches the proof exactly, on Sellat or with open tools.
The proof identifies the file by its exact content: change a single byte and the fingerprint changes and no longer matches.
When it is used
Before you send it.
The useful moment is always the same: just before the document leaves your hands.
The quote, before you send it
There is a record of the figures and conditions in the version you sent, even if a different one is discussed later.
The contract, before you sign it
The version that was negotiated is identified, even if similar copies circulate afterwards.
The report or deliverable, before you hand it over
It fixes what you delivered and the date you had it finished.
The annex, before you argue about it
If another version turns up months later, the fingerprint says which is which without relying on anyone’s memory.
Scope
What it proves, and what it does not.
What it proves
That this exact content existed on the date of the proof and has not changed since. That is what lets you tell one version from another.
What it does not prove
It does not prove authorship or ownership, it does not prove that what the document says is true, and it does not replace any public register. Its weight is for the judge to assess in each case.
Price
Creating the proof costs nothing
Protecting a document and receiving its certificate is free. The qualified timestamp is optional and is added from the certificate. Your first qualified timestamp is free. One per account, on the proof you choose. After that, €6 per timestamp.
If you need a legal presumption, add a qualified timestamp issued by the FNMT-RCM: the first one is free → Certify a documentFrequently asked questions
Before you ask.
Does it work for a PDF that is already signed?
Yes. The proof is computed over the file as it is, signature included. What is recorded is that exact file on that date, not the content of the agreement or who signed it.
What if I change a comma afterwards?
You will have another file, with another fingerprint, which no longer matches the proof. If you want the new version on record too, protect it as well: two proofs, two dates.
Is it the same as a certified date?
Not quite. Sellat records that this exact file existed at a given moment, and with a qualified timestamp that date carries the legal presumption of article 41.2 of Regulation (EU) 910/2014. Whether a specific procedure’s requirement for a certified date is met is for a lawyer or the judge in the case to assess.
Is it legally valid?
Electronic evidence cannot be dismissed solely for being digital: that is article 41.1 of Regulation (EU) 910/2014. What counts is what the judge makes of it in each case, and what the proof contributes is a date and an integrity anyone can check.
Do you keep my document?
Without an account, the file is uploaded to generate the certificate and the verification package. With a free account you can use Sellat Local: the fingerprint is computed on your device and the original is not uploaded. Keeping the file at Sellat (custody) is a separate, optional choice you switch on deliberately.
What exactly do I receive?
A PDF certificate and a ZIP with the file you protected, the verification data and the instructions to check it. If you add the qualified timestamp, the package also carries the timestamp (.tsr) and the certificate of the authority that issued it.
How much does certifying a document cost?
Creating the proof and receiving the certificate costs nothing. The qualified timestamp is the only thing you pay for. Your first qualified timestamp is free. One per account, on the proof you choose. After that, €6 per timestamp.