How to use
- Choose or drop a signed PDF.
- Read the result for each signature — valid, changed after signing, invalid, or could not be verified.
- Open Signer certificate and Certificate chain for the full details, and download the certificate if you need it.
Options explained
- Valid — not changed since it was signed
- The signed bytes match the signature, the signature matches the signer’s certificate, and nothing was added to the file afterwards.
- Valid, but the file was changed after signing
- The signature itself is fine, but later revisions were appended — often legitimate, such as filling in a form or adding another signature, but worth checking in a PDF reader.
- Invalid
- The content no longer matches the signature, the signature does not match the certificate, or part of the file is not protected by the signature.
What the results mean
| Result | Meaning | What to do |
|---|---|---|
| Valid — not changed since it was signed | The signed bytes match the signature, the signature matches the certificate, and nothing was added later | Check that the signer’s name and certificate issuer are who you expect |
| Valid, but the file was changed after signing | The signature covers an earlier version; later revisions were appended, such as filled-in form fields, comments or another signature | Normal for forms and multi-signer documents; if you did not expect changes, ask the sender |
| Invalid | The content no longer matches the signature, or the signature does not match the certificate, or part of the file is not covered | Do not rely on the document; ask for the original |
| Could not be verified | The signature data is damaged or uses an algorithm the tool does not support | The certificate details are still shown; check it in Adobe Acrobat Reader |
What is checked, and what is not
Checked: that the bytes covered by each signature are unchanged; that the signature value matches the signer’s public key (RSA, RSA-PSS, ECDSA and SM2); RFC 3161 timestamps; and whether any bytes in the file are left outside the signature.
Not checked: whether the certificate is trusted by your country or company, and whether it was revoked. The tool shows the issuer and the certificate chain included in the PDF — use them to decide whether you trust the signer, or open the file in Adobe Acrobat Reader, which checks against its trust list.
Signing time. A time shown as “proven by a timestamp” comes from an independent timestamp authority. Without one, the time comes from the signer’s own computer and could be set to anything.
Frequently asked questions
Does a valid result mean the signer is who they claim to be?
It means the file was not altered and was signed with the private key of that certificate. Whether the certificate itself is trusted — issued by a recognised authority and not revoked — needs Adobe Acrobat Reader or the issuing authority’s verification service, because that requires online checks.
The tool says the PDF has no digital signature, but I can see a signature on the page. Why?
A scanned or pasted image of a handwritten signature or stamp is just a picture. Only a cryptographic digital signature can show whether the file was changed.
Is my PDF uploaded?
No. The signatures are checked in your browser.
Privacy
This tool runs entirely in your browser. Your files and text are processed on your device and are never uploaded to our servers.