How do I check that a signed PDF has not been modified?
Drop the document: we read every signature it contains and give a separate verdict for each — content unchanged or not, signature matching the certificate or not.
Check a signature
Check that a signed PDF has not been altered since.
Drop in a signed or sealed document: we read every signature it carries and report on each separately. You will see what is established — the content has not changed, the signature matches the certificate — and what is not. No account, no key, free.
The document is sent so we can read the signatures it carries, then deleted. No account needed.
What “valid signature” means
Verification answers two distinct questions, and conflating them is the source of almost every misunderstanding on the subject.
First: has the content covered by the signature moved since it was applied? That is a mathematical question, and the answer is yes or no, with no shading. Second: does the signature actually match the certificate it presents? That is what ties the document to an issuer.
We report separately on every signature in the document, and we separate what is established from what is not. A document may carry several — signed, then countersigned, then sealed — and one can hold while another has failed.
What verification does not tell you
It does not tell you the document is true. A dishonest contract, properly sealed, yields a perfectly valid signature: verification attests that nobody has retouched the lie since, not that it is accurate.
Nor does it tell you the signer was authorised to sign. A certificate identifies an organisation or a person, not their powers.
Finally, a change made after signing does not always invalidate everything: a PDF allows successive updates, and it is normal for a document that was sealed and later annotated to keep a valid seal on its original revision. That is why the report states what was covered.
No account, no key, free
The file is sent to our servers in Europe — reading a certificate needs libraries that have no place in a browser — then deleted like every other.
But verification consumes no quota and requires no account, while sealing requires one. The imbalance is deliberate: refusing to let someone check a document you handed them would make no sense, and a guarantee only the issuer can verify is not a guarantee.
Common questions
Do I need an account or a key to check?
Neither. Checking is open and free, with no quota: it is something we want to encourage, not bill for.
What does this check not tell me?
It establishes the document's integrity and the signature's validity. It does not say whether the certificate belongs to a recognised authority — that is a matter of trust, not computation.
What happens to my file afterwards?
This tool needs a machine: your file is sent to our servers in Europe, processed, then deleted automatically. We keep no copy and we do not read it.