How do I know if a digital signature on a contract is valid?

Open the PDF in Acrobat. Click the digital signature. Select 'Validate Signature' from the options. Acrobat will show you if the signature is valid and if the document was changed.

If a digital signature says 'unknown validity', what should I do?

Check your 'Trusted Identities' settings in Acrobat to make sure the signer's certificate is listed and trusted. Contact the signer to ask them to provide a valid certificate or re-sign the document. The signature might be old, so adding 'Long-Term Validation' (LTV) information could help if the original certificate was valid.

How is verifying a digital signature different from just looking at a scanned signature image?

Feature Digital Signature Verification Scanned Signature Image. Purpose Confirms signer identity and document integrity (no changes). Shows a picture of a signature, but proves nothing about identity or changes. Security Uses cryptography to link signer to document, highly secure. Can be easily copied or faked, offers no security. Trust Relies on trusted certificates and validation processes. Relies only on visual appearance, no built-in trust.

Unauthorized Contract Changes in Adobe Acrobat — How-to & AI prompts

AI prompts

2 ways to ask · copy any one

CDecide — “help me choose”After a suspected breach, I ran an audit trail and have raw access logs for critical contracts…+

After a suspected breach, I ran an audit trail and have raw access logs for critical contracts but I can't tell which entries are routine and which indicate tampering. Review the trail for last 10 days, identify anomalous access or modification patterns (off-hours edits, unfamiliar accounts, unusual IPs), state the likely explanations (benign admin action, misconfigured sync, or malicious access), and give the immediate steps I should tell Legal and IT to take before the incident call.

when the reply comes backPush once: ask it to sharpen the weakest part, and to say what it assumed.

DBecome — “help me grow”In two recent vendor contracts, an unapproved payment term caused a payment dispute. Recommend…+

In two recent vendor contracts, an unapproved payment term caused a payment dispute. Recommend a repeatable preflight checklist and a comparison routine that PMs can run before routing to legal so substantive changes are always caught. Describe the top three contract clauses that should trigger an immediate legal review

when the reply comes backPush once: ask it to sharpen the weakest part, and to say what it assumed.

How to do it

the tool · the steps · what to avoid

1
Open the PDF document containing the digital signature you want to validate.
2
If prompted, enable all necessary trust settings for the certificate authority used by the signature.
CautionIf the certificate is not trusted, Acrobat may not be able to validate the signature correctly.
3
Look for the Signatures panel on the right side, or click on the signature field in the document to open the signature details.
4
In the Signatures panel or details dialog, review the signature status message to check if the signature is still valid after document changes.
NoteAcrobat will indicate if the document was modified after signing and whether the changes are permitted (such as filling in forms or adding approved annotations) or if the signature was invalidated by unauthorized edits.
5
Expand the signature properties to view the list of changes made after signing, if any.
Best practiceClicking 'View Signed Version' lets you compare the signed state to the current version to see exactly what changed.
6
Confirm whether the signature remains valid or has been invalidated by edits, as indicated by Acrobat.

In the appWith the API

You can quickly check if a signature is still valid after changes by opening the signature panel and reviewing the status message.

This runs in the Acrobat app - there is no separate API for this task.

Glossary

words on this page

Digital SignatureAn electronic mark on a document that proves who signed it and that the document has not changed.ExampleA digital signature on your tax return confirms you submitted it and that its contents are unchanged.

CertificateAn electronic file that proves a person's or organization's identity online, like a digital ID card.ExampleYour certificate confirms your identity when you access secure online government services.

Trust RelationshipWhen your computer or software believes a digital certificate is real and safe to use.ExampleYour browser forms a trust relationship with a secure website to protect your online banking session.

The real tasks

all 2, listed here

Security incident: contract files were altered and I must know who touched them before tonight's call.

Unauthorized contract changes occasionally slip past and create surprises later.

FAQ

about this task

Open the PDF in Acrobat.
Click the digital signature.
Select 'Validate Signature' from the options.
Acrobat will show you if the signature is valid and if the document was changed.

A certificate trust means your computer or Acrobat recognizes and believes the digital ID of the person who signed the document. It matters because if you don't trust the certificate, you cannot be sure the signature is real or that the document has not been tampered with. It's like checking if an ID card is from a real government agency.

Check your 'Trusted Identities' settings in Acrobat to make sure the signer's certificate is listed and trusted.
Contact the signer to ask them to provide a valid certificate or re-sign the document.
The signature might be old, so adding 'Long-Term Validation' (LTV) information could help if the original certificate was valid.

Adding Long-Term Validation (LTV) information is important because it makes sure the digital signature remains valid and verifiable long into the future. Without LTV, a signature might become invalid over time if the original signing certificate expires or is revoked. LTV embeds all the necessary validation data directly into the document, so you can always confirm the signature's status, even years later, without needing external information.

Feature	Digital Signature Verification	Scanned Signature Image
Purpose	Confirms signer identity and document integrity (no changes).	Shows a picture of a signature, but proves nothing about identity or changes.
Security	Uses cryptography to link signer to document, highly secure.	Can be easily copied or faked, offers no security.
Trust	Relies on trusted certificates and validation processes.	Relies only on visual appearance, no built-in trust.

Unauthorized Contract Changes

When to use it

AI prompts

How to do it

Glossary

The real tasks

Who does this

FAQ

Sources

Adobe help