What does a valid signature mean?

That the content the signature covers is exactly as it was when signed, and that the signature matches the certificate inside it. It doesn't by itself prove who the signer is: that depends on whether you trust the certificate.

Does it check whether the certificate is trusted or revoked?

No. That needs trust lists and revocation servers run by other sites, and contacting them would mean sending details of your file elsewhere. Use a reader such as Adobe Acrobat Reader when you need that check.

Why does it say my PDF has no signatures?

A signature that was drawn, typed or pasted as a picture is only an image on the page. Only a digital signature, made with a certificate, can be checked. Sign PDF can add one if you have a certificate file.

What if the file was changed after signing?

The signature still covers its own version, so it can be valid while later changes, such as added comments or filled fields, are not covered by it. The report says so; ask the sender whether those changes were expected.

Are timestamps checked?

A timestamp from a timestamping authority is shown when the signature includes one, but its own signature isn't checked. The signing time shown comes from the signer's computer.

Check PDF signatures

See who digitally signed a PDF, whether the signature is intact, and whether the file changed after signing.

Runs on your device

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How to use Check PDF signatures

01Add one signed PDF.
02The report appears straight away, with one entry for each signature or timestamp in the file.
03Read each signature's status and details, and whether the file changed after it was signed.

About Check PDF signatures

Check PDF signatures opens a signed PDF and reports on every digital signature in it. For each one you see whether the signature is valid, who signed, which certificate was used and who issued it, the signing time the signer's computer gave, and the reason and location if the signer filled them in. It also tells you whether anything was added to the file after it was signed: a later comment, a filled field or another signature. A PDF can be signed several times, and each signature only covers the version that existed when it was made, so each one is checked against its own part of the file. The check runs in your browser and works with the common PDF signature formats, including PAdES signatures made with Sign PDF.

Why your files stay private

Signed documents are often contracts, invoices and official letters. Here the file is opened and checked in your browser; no part of it, not even the certificate details, is sent to a server, and Nopload keeps no record of it.