Someone sends you a "signed" contract. You can see a signature image at the bottom. Is that a real digital signature, or just a JPEG of a scribble?
The difference matters legally. A digital signature carries a cryptographic certificate. A pasted image is decoration.
Look for the signature panel
Open the PDF in Adobe Reader or a desktop reader. Look for a Signatures panel on the left sidebar, or a banner at the top reading "Signed and all signatures are valid".
No panel, no banner — there's no digital signature. There may be a signature graphic on the page, but it carries no verification.
Inspect the certificate
Click the signature in the panel to see details. A valid digital signature shows: the signer's name and certificate, the signing time, what was signed (the document hash), and whether anything has changed since signing.
If the certificate is from a trusted authority (DocuSign, Adobe Sign, a recognised CA) and the document hasn't been altered, the signature is valid. If anything's been changed post-signing, the reader will flag it.
What to do if it's not really signed
An image-only signature is fine for internal use but not legally binding in most jurisdictions. If you need a verifiable signature, ask the sender to re-sign using a proper signing tool.
For your own outbound signing, use Flint's signing tool — it creates a verifiable signature with an audit trail, not just a pasted graphic.
FAQ
What's the difference between a digital signature and an electronic signature?
Electronic signatures are any sign-off — pasted image, typed name, drawn signature. Digital signatures are a specific cryptographic form with a certificate and tamper detection. Both can be legally binding depending on jurisdiction.
Why does my signed PDF say "signature validity unknown"?
The signature's certificate isn't recognised by your reader. Sometimes it's expired; sometimes it's from an authority the reader doesn't trust. Doesn't mean the signature is fake — but it can't be auto-verified.
Can I sign a PDF that's already been signed?
Yes — multiple signatures stack. Each adds a layer to the audit trail. Use Flint's signing tool to add yours.
Will the signature be removed if I edit the PDF?
Editing invalidates the signature. The signature panel will show that the document has been modified since signing.
Verifying a signature takes 30 seconds. For signing new documents with real verification, use Flint's signing tool — it does what a pasted image can't.