How to Fix “At Least One Signature Has Problems” in Adobe Acrobat

To fix “At least one signature has problems” in Adobe Acrobat, open the PDF’s Signatures panel, validate the affected signature, and read Signature Properties before changing anything. The message does not automatically mean the PDF was tampered with. Acrobat may be unable to trust the signer, check revocation, verify a timestamp, or confirm the signed content. Keep the original PDF unchanged and use the seven checks below to identify the right fix.

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What “At Least One Signature Has Problems” Actually Means

A certificate-based digital signature helps Acrobat check whether signed content has changed and whether the signing certificate can be linked to a trusted identity. It differs from a pasted signature image or other types of electronic signature.

The warning summarizes a validation problem, possibly affecting only one of several signatures.

Acrobat’s Finding	What It Means	What to Check Next
Signer identity or validity is unknown	Acrobat lacks enough trusted evidence to complete validation	Signer’s certificate, issuer, trust chain, and verification data
Signed content is altered or corrupted	The signed content failed an integrity check	Signed revision versus current PDF; obtain an original if necessary
Changes occurred after signing	The PDF has later revisions, which may or may not be permitted	Signature permissions and what changed
Certificate has expired	A certificate is outside its validity dates at the time being evaluated	Verified signing time and trusted timestamp
Certificate is revoked	Revocation evidence reports a problem with the certificate	Applicable verification time and issuing authority
Revocation status cannot be determined	Required evidence could not be retrieved or verified	Network access, certificate chain, and available revocation data

Unknown is not the same as invalid. An unknown signer may have signed unchanged content. Trusting their certificate cannot repair altered content.

How to Fix “At Least One Signature Has Problems” in 7 Steps

Step 1. Preserve the Original PDF and Open It in Desktop Acrobat

Save the original attachment or download unchanged and investigate a separate copy. Do not edit, flatten, compress, print to a new PDF, or remove its signature fields.

Open the file in Adobe Acrobat or Acrobat Reader on your computer, rather than relying only on a browser or email preview. Viewer support differs, so a missing browser warning does not prove validity.

If the PDF was forwarded or converted, ask the original sender for the unmodified signed file.

Result to look for: The original is preserved, and you have a copy open in a viewer with Acrobat’s signature-validation controls.

Step 2. Find the Affected Signature in the Signatures Panel

In the current Acrobat desktop interface:

1. Select Signatures from the side panel.
2. Expand the signature entries. Check each one if the document has multiple signers.
3. Select the affected signature, open Options, and choose Validate Signatures or the corresponding validation command shown for that selection.
4. Read the Signature Validation Status dialog, then open Signature Properties for more detail.

To check them all, use All tools > Use a certificate > Validate all signatures. Interface layouts vary.

Do not stop at the banner or a colored icon. Read the status text to find out whether Acrobat is questioning the document’s integrity, the signer’s identity, the certificate’s validity period, the timestamp, or revocation information.

One signer can be trusted while another remains unknown. Check them individually.

Result to look for: You can name the affected signature and the specific validation issue, rather than guessing from the general warning.

Step 3. Check Whether the Signed PDF Was Changed

Open Signature Properties for the affected signature and review the document-integrity summary. Then, if the option is available in your Acrobat edition, follow:

Signatures > Select the signature > Options > Compare Signed Version to Current Version

If the comparison command is unavailable in your edition, ask the sender or administrator for an appropriate comparison. Do not edit the file yourself.

Three outcomes need different treatment:

• No signed-content changes, but signer unknown: Investigate certificate trust in Step 4. Do not assume tampering.
• Later changes exist: Determine whether the signature or certification permitted them. An additional signature or an allowed form update is not automatically equivalent to unauthorized editing.
• Signed content fails integrity validation: Stop treating that signature as verified. Request an unchanged original or an appropriately signed replacement from the sender.

Hypothetical example: A certified form may permit designated field entries, but replacing a signed paragraph is different. Check the actual permissions and validation result.

Read more about what happens when you edit a signed PDF. Changing certificate trust cannot restore altered signed content.

Step 4. Inspect the Signer’s Certificate and Trust Chain

From the Signatures panel, select the signature and open Options > Show Signature Properties > Show Signer’s Certificate.

Inspect the certificate information, including:

• Subject: The identity claimed by the certificate.
• Issuer: The authority that issued it.
• Certificate path: Any intermediate authorities and root certificate.
• Validity dates: When the certificate was issued for use.
• Fingerprint and trust details: Information you can use when confirming the certificate with an independently known contact.

A familiar name alone is insufficient. Acrobat may not recognize a corporate authority, an intermediate may be missing, or the certificate may be self-signed.

For unknown signers, confirm identity and certificate fingerprint through an independently known contact or IT. Do not rely solely on details in the suspect PDF or email.

An appropriate certificate chain may be needed, but do not blindly click “Add to Trusted Certificates.” Root trust can cover other certificates issued beneath it. Consult IT for organizational trust decisions.

Result to look for: You know whether the trust path is incomplete, locally untrusted, or genuinely verified through an appropriate authority.

Step 5. Check Certificate Expiration and the Trusted Timestamp

The date you open a PDF is not always the relevant signature-verification time.

In Signature Properties, inspect the reported signing time and timestamp status. Acrobat may indicate that the time came from the signer’s computer clock, that the signature has a trusted timestamp, or that the timestamp could not be verified.

Distinguish:

• Computer clock time: The signer-controlled device supplied the time. By itself, this is not independent proof of when signing happened.
• Verified trusted timestamp: A timestamp authority provides independent time evidence that Acrobat can verify under the applicable trust settings.
• Unverifiable timestamp: Timestamp information exists, but its trust or verification could not be established.

Hypothetical example: A certificate was valid from January 2023 through January 2025. A PDF says it was signed in October 2024, and you open it in 2026. The certificate’s current expiration does not by itself settle whether the historical signature was valid. A verified trusted timestamp from October 2024, together with suitable certificate and revocation evidence, can affect the result. A date copied from the signer’s computer clock is weaker evidence.

A timestamp authority can also have certificate or validation problems. Do not change verification preferences merely to remove warnings.

Result to look for: You understand which time Acrobat can actually verify and whether expiration is relevant to that assessment.

Step 6. Check Revocation Status Without Disabling the Check

Certificates can be revoked before expiration. Acrobat may check a CRL or OCSP response, taking account of the verification context.

Review the certificate and signature-validation details. Distinguish two situations:

The certificate is reported as revoked. Do not bypass this finding or rely on the visible signature image. Contact the signer or issuer and request a replacement where appropriate.

Revocation status is unavailable or cannot be determined. Acrobat may lack verification data, service access, or a complete chain. Retry online validation; ask IT about blocked services or the sender for suitable long-term validation evidence.

Keep certificate revocation checking enabled. Disabling it only hides an unresolved question.

Result to look for: You know whether revocation was established, ruled out for the applicable verification context, or remains unknown.

Step 7. Apply the Fix That Matches the Validation Result

Match the action to the result:

Confirmed Problem	Appropriate Next Action
Trusted authority information may be outdated	In Preferences > Trust Manager, look for the Adobe Approved Trust List (AATL) update controls and select Update Now where available. Revalidate afterward.
Missing or untrusted certificate chain	Independently verify the signer, then obtain the appropriate chain from a trusted issuer or your IT administrator. Establish only the trust needed for that verified workflow.
Signed-content integrity failure	Request the unchanged original or an appropriately signed replacement. Do not attempt to fix this with certificate preferences.
Certificate expired or timestamp uncertain	Examine the trusted signing time and historical evidence; ask the sender or issuing organization for suitable verification information.
Certificate revoked	Do not override the finding. Ask the signer or issuer to resolve it and provide a suitable replacement when needed.
Revocation evidence unavailable	Restore access to the verification service or request available validation evidence. Keep revocation checks enabled.
Limited viewer support	Validate the original in desktop Acrobat or another suitable signature validator rather than drawing conclusions from a preview.

AATL and European Union Trusted Lists do not cover every organizational certificate. Updating them is not a guaranteed fix. Avoid enabling blanket trust for all Windows root certificates.

After a justified fix, validate again. Review integrity, identity, timestamp, and revocation findings, not just the banner.

What to Request if the Warning Still Appears

If validation remains unresolved, request evidence matching the problem:

Remaining Problem	Ask the Sender or Administrator For
Identity cannot be established	Confirmation of the signer through an independently known contact, plus an appropriate certificate chain or verified fingerprint
Signed content was altered	The original unchanged signed PDF or a newly signed replacement
Timestamp cannot be verified	Timestamp-authority details and available historical validation evidence
Certificate was revoked	An explanation from the issuing organization and an appropriately signed replacement if needed
Revocation data cannot be retrieved	Network assistance or available long-term validation information

Avoid unknown online PDF repair services. Practice only with dummy documents and a self-owned test certificate.

Why the Same PDF May Validate on One Computer but Not Another

Acrobat installations can differ in trusted roots, trust-list updates, and access to revocation services. Other PDF viewers may use different validation paths.

Hypothetical example: A company sends a digitally signed document using its internal certificate authority. The sender’s laptop trusts that authority, so the signature can validate there. An outside recipient’s Acrobat does not recognize the authority and reports that the signer’s identity is unknown. The recipient must independently verify the identity and trust path.

This may apply to platform-generated PDFs, including some DocuSign workflows. Inspect the actual certificate.

FAQ

What Does “At Least One Signature Has Problems” Mean in Adobe Acrobat?

It means Acrobat could not fully validate at least one digital signature. The reason may involve certificate trust, document integrity, expiration, a timestamp, or revocation information. Open the Signatures panel and inspect Signature Properties to identify the actual issue before deciding whether the PDF can be relied on.

Does This Adobe Acrobat Warning Mean My PDF Was Tampered With?

Not necessarily. An unchanged PDF can display this warning if Acrobat cannot establish trust in the signer or retrieve verification data. Check the signed-content status separately. If Acrobat explicitly reports altered or corrupted signed content, preserve the file and request an unchanged original or properly signed replacement.

How Do I Open the Signatures Panel in Adobe Acrobat Reader?

Open the PDF in desktop Acrobat Reader and select Signatures from the side panel. Expand the relevant signature, open its options, and view the validation status or properties. The exact panel location can vary with the interface version. If you cannot find it, look for the signature indicator in the PDF’s document bar.

Why Does Adobe Acrobat Say “Signature Validity Is Unknown”?

Acrobat may lack a trusted certificate path, independently verifiable identity, usable timestamp, or revocation evidence. Unknown validity does not automatically mean the cryptographic signature failed. Inspect the detailed validation message and certificate chain, then obtain reliable evidence from the sender or certificate administrator before changing trust settings.

Should I Click “Add to Trusted Certificates” to Fix the Warning?

Only after you have independently verified the certificate and understand the scope of the trust you are granting. Do not trust an unknown signer just to clear a warning. Trusting a certificate as a root can also extend trust to certificates issued beneath it, so organizational changes may require IT approval.

Can a Digital Signature Still Be Valid if the Signer’s Certificate Has Expired?

Yes, depending on the verified signing time and applicable validation evidence. A trusted timestamp can show that signing occurred while the certificate was valid, even if the certificate has since expired. Acrobat also needs appropriate trust and revocation information. A date taken only from the signer’s computer is not equivalent to a verified timestamp.

What if Acrobat Cannot Check Whether a Certificate Has Been Revoked?

Treat the revocation status as unresolved, not as proof that the certificate is revoked or valid. Check your connection, the certificate chain, and access to verification services. Ask IT or the sender for help obtaining suitable evidence. Do not disable revocation checking to force a successful validation result.

Why Is a Digital Signature Valid on the Sender’s Computer but Not Mine?

The computers may trust different certificate authorities, have different trust-list updates, or reach different verification services. The sender may already trust an internal certificate authority that your Acrobat does not recognize. Compare the actual signature details and verify the signer independently before making local trust changes.

What Should I Do if Acrobat Says a Signed PDF Was Altered or Corrupted?

Preserve the file and inspect the signature’s document-integrity details. If the signed content genuinely fails verification, do not try to repair the result by importing a certificate. Request the unchanged signed original or a replacement from the sender. A visible signature graphic cannot validate content that fails its integrity check.

Why Does a DocuSign-Signed PDF Show a Signature Warning in Adobe Acrobat?

Some DocuSign-related warnings concern the certificate trust path Acrobat uses to validate a platform signature or seal. That is different from proving a particular person’s identity through the signature alone. Inspect the actual certificate and integrity details. If the trust chain is unfamiliar, verify it through an official, independent channel before trusting it.