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PDF Signature Checker
Instantly verify digital signatures and ensure document integrity. Detect unauthorized modifications and validate signer identities without uploading your files.
Drag & Drop Signed PDF
Or check verify document integrity instantly. Client-side only.
What is PDF Signature Checker?
In the digital age, **document integrity** is paramount. Our **PDF Signature Checker** allows you to mathematically verify that a signed PDF has not been tampered with since it was signed. By analyzing the cryptographic hash embedded in the signature (PKCS#7/CMS) and comparing it to the actual file content, we provide an instant assessment of validity.
How to Use PDF Signature Checker
1
**Upload Signed PDF**: Drag and drop your digitally signed PDF file into the secure zone.
2
**Automatic Analysis**: The tool instantly parses the file structure to locate digital signature dictionaries.
3
**Cryptographic Verification**: We re-calculate the file hash (SHA-256/SHA-512) and compare it against the signed digest.
4
**Review Report**: See a clear status indicating if the signature is valid (integrity intact) or invalid (tampered).
Key Features
**Tamper Detection**: Uses math to detect even a single byte change in the document.
**Signer Identity extraction**: View the Common Name (CN) and other certificate details of the signer.
**Client-Side Privacy**: Your sensitive contracts and legal documents never leave your browser.
**Multi-Signature Support**: Detects and verifies multiple signatures within a single document.
**Instant Results**: No waiting for server uploads or processing queues.
About PDF Signature Checker
Why Verify Digital Signatures?
A digital signature is more than just an image of a handwritten signature. It is a cryptographic seal that binds an identity to a document's content. If a single comma is changed in the contract after signing, the signature acts as a tamper-evident seal and breaks.
- Integrity: Proof that the document has not been altered.
- Authenticity: Proof of who signed the document (via Certificate).
- Non-Repudiation: The signer cannot deny having signed it.
How It Works (The Tech)
When a PDF is signed, a "digest" (hash) of the file content is created. This digest is encrypted using the signer's **Private Key**. This tool:
- Extracts the encrypted digest from the PDF signature dictionary.
- Decrypts it using the public key found in the certificate.
- Independently calculates the hash of the file you uploaded.
- Compares the two hashes. If they match, the document is pristine.
Frequently Asked Questions
Is my document uploaded to a server?
No. This tool operates entirely in your web browser. We use advanced JavaScript libraries (node-forge) to perform cryptographic operations locally on your device. Your files remain private.
Why does Adobe Acrobat show 'Unknown Trust' but this tool says 'Valid'?
Adobe validates against a specific 'Trusted List' (AATL) of government and corporate issuers. Browsers do not have access to this proprietary list. Our tool verifies the **mathematical integrity** (the file hasn't been changed) and displays the identity, but cannot verify if the issuer is specifically trusted by Adobe.
Can I verify DocuSign or Adobe Sign signatures?
Yes. Assuming the PDF contains a standard PAdES (PDF Advanced Electronic Signatures) standard signature, our tool can detect and verify its integrity.