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What a digital signature can prove
A certificate-based PDF signature is cryptographic information, not just a picture of a signature. When validation succeeds, it can help establish two things: the signed content has not been altered since that revision was signed, and the signer’s certificate identifies a signer trusted under the verifier’s trust configuration. NIST describes digital signatures as a way to detect unauthorized data changes and authenticate a signatory’s identity in FIPS 186-5 (2023).
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Those conclusions are conditional. The verifier must evaluate the signature and certificate chain, and the relevant trust policy must accept that chain. A visible signature graphic, a date printed on the page, or a green icon by itself does not establish cryptographic validity or universal trust.
How to verify a signed PDF in Acrobat
Adobe’s validation guidance describes checking signatures in Acrobat and reviewing the signer and certificate details. Product labels or behavior can change, so use the current Acrobat interface and report the status it actually displays. Adobe’s instructions were last updated on 5 November 2025: Validate digital signatures in Adobe Acrobat.
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- Open the signature details. In Acrobat, open the PDF and select the Signatures panel. Review the listed signatures rather than relying on a visible mark on the page.
- Validate the signature. Use Acrobat’s validation action for the signature, then note the result and any warnings. Check whether Acrobat reports the signature as valid, whether the document was changed after signing, and whether the certificate chain is trusted.
- Inspect the signer’s certificate. Review the certificate identity and chain, including whether the issuer and trust status are acceptable for your organization’s policy. A validator’s “valid” result is a conclusion under its configuration, not a blanket legal finding.
- Check the signed revision. A signature applies to a particular document revision. If the PDF has later permitted updates or additional signatures, inspect revision details to determine what was covered by the signature you are evaluating.
- Read the timestamp status precisely. Determine whether the displayed time comes from the signer’s computer clock or a trusted timestamp, and whether Acrobat can verify the timestamp authority’s certificate.
Adobe explains certificate signatures, signer identity, integrity, timestamps, and long-term validation in About certificate signatures in Adobe Acrobat. Validation is only as meaningful as the trust sources and evidence available to the verifier.
Can you trust the timestamp?
Not every date associated with a signature is independent evidence of when the signing key was used. A time supplied by the signer’s computer reflects that computer’s clock. Elaine B. Barker, author of NIST SP 800-102, published 23 September 2009, states: “A signed message that includes the (purported) signing time provides no assurance that the private key was used to sign the message at that time unless the accuracy of the time can be trusted.”
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A trusted timestamp can provide stronger time assurance when it comes from a timestamp authority whose certificate the verifier trusts. Barker says that an appropriately used digital-signature timestamp from a Trusted Timestamp Authority, and/or verifier-supplied data included in the signed message, can provide “some level of assurance” about signing time. The phrase matters: it is assurance under the applicable verification conditions, not proof beyond all doubt.
Acrobat may distinguish a trusted timestamp from a timestamp that is present but unverifiable—for example, because the timestamp authority’s certificate is unavailable, untrusted, or expired. Record the displayed state; the presence of a date alone does not show that the timestamp validates.
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What the signature does not prove about marketplace data
Signature validation concerns the signed PDF, its signer credential, and the verifier’s trust policy. It does not independently confirm that the marketplace platform produced the report, that the collection process was sound, that the records are complete, that calculations are correct, or that the report’s claims are true. Those are separate questions about data provenance and methodology, not conclusions supplied by cryptographic validation.
For a defensible archive, retain the underlying source exports alongside the signed report, with collection timestamps and notes identifying the methodology and its version. Preserve a clear relationship between those materials and the report so a later reviewer can check the data rather than merely the integrity of the PDF.
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Use a precise description when communicating a result: “The signature validated using [named verifier and trust configuration], and the signed PDF revision showed [reported change status]. This supports the integrity of that revision and the signer certificate identity; it does not independently verify the underlying marketplace claims.”
Preserving a signed report for later verification
A PDF that validates today may be harder to validate in the future if the certificate expires or revocation information is no longer available. Adobe describes long-term validation as relying on evidence such as the certificate chain, revocation status, and timestamp, which may be embedded in or retained with the document. Its overview of long-term validation is vendor guidance; archive policies should account for the software and trust requirements in use.
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- Keep the original signed PDF unchanged. Do not rewrite or resave it in a way that replaces the signed file.
- Retain validation reports and relevant certificate, revocation, and timestamp evidence where your policy permits.
- Record the verification date, software and version, trust configuration, and timestamp authority or trust context used.
- Preserve the marketplace source exports, collection-time evidence, and methodology/version notes with clear links to the signed report.
- If later updates are permitted, retain revision history and identify which revision each signature covers.
Adobe discusses retained validation information and certificate expiry in its 30 June 2022 explanation of long-term validation. Long-term preservation supports future checking; it does not establish indefinite validity or legal admissibility, which depend on applicable rules and circumstances.
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