How can I verify if a PDF document has been modified?

By calculating the SHA-256 cryptographic hash of the document. Any alteration, even a single space or pixel, drastically changes the 64-character hash code. Comparing the current hash with the original proves whether alterations occurred.

Are my files uploaded to any server during verification?

No. PDFListo calculates the SHA-256 hash entirely in your device memory via the browser native WebCrypto API. Zero bytes are uploaded to the internet.

🛡️ Auditoría Forense Criptográfica • Local-First

Verify PDF Digital Signature & Integrity Online

Calculá el hash SHA-256 matemático de cualquier documento, comprobá si ha sido alterado y auditá metadatos de autoría y firmas sin subir el archivo a ningún servidor.

Respuesta Rápida: Para verificar si un documento PDF es auténtico y no fue modificado, subí el archivo a PDFListo. El motor criptográfico calcula de forma 100% local el hash SHA-256 inmutable y analiza los metadatos de firma. Si el hash coincide con el certificado original, el documento es 100% íntegro.

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Drag & drop any PDF document to audit its integrity

Analysis runs 100% in your device's memory via WebCrypto API. Zero bytes sent to the cloud.

Cryptographic Audit & Tamper Detection in PDF Documents

In legal, financial, and regulatory workflows, verifying whether a digital document has been modified after execution is essential to prevent fraud, unauthorized edits, or page replacements. Traditional visual reviews are insufficient because digital files can be altered without obvious aesthetic artifacts.

Why the SHA-256 Algorithm is the Forensic Gold Standard

The Secure Hash Algorithm 256-bit (SHA-256) is a cryptographic one-way hash function standardized by the NIST (FIPS 180-4). It exhibits what cryptographers call the avalanche effect:

If a 500-page document undergoes the change of a single letter, invisible whitespace, or metadata attribute, the resulting hash changes drastically across more than 50% of its characters.
It is computationally infeasible for two different documents to produce the exact same digital fingerprint (collision resistance).
It enables courts, forensic auditors, and commercial parties to verify mathematical authenticity beyond all doubt.

Legal Framework & Evidentiary Value

Integrity verification through cryptographic hashing and timestamps is recognized under modern digital legislation:

United States (Federal Rules of Evidence Rule 902(13) & (14)): Permits self-authentication of electronic records through process certifications utilizing cryptographic hash values.
European Union (eIDAS Regulation 910/2014): Establishes the admissibility of electronic evidence reinforced by integrity hashes and qualified timestamps.
ESIGN Act & UETA: Validates electronic records and contracts where integrity and intent can be reliably proven.

Frequently Asked Questions on Forensic Verification

What does it mean if the hash matches?

It means the document in your possession is byte-for-byte identical to the version that generated the reference hash, with zero modifications since the time of certification.

Can I audit confidential client or patient files?

Yes. The entire audit is executed inside your own browser memory via the WebCrypto API. No files are transmitted across the network or stored on remote servers.

How do I create a verifiable timestamp seal when signing?

You can use our companion tool at /en/sign-pdf, which automatically computes the document SHA-256 hash and stamps it alongside the UTC timestamp and biometric or drawn signature.

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