Never trust a modified contract. Cryptographically verify digital signatures and X.509 certificates to prove a PDF document has not been tampered with.
Drop a PDF here or click to upload
Supports PDF files only
Execute PKI certificate validation to ensure the legal integrity of your enterprise documents.
The engine recalculates the SHA-256 hash of the document's raw bytes and compares it against the encrypted hash locked inside the signature block. If they mismatch, the document was altered.
Instantly extract the X.509 Public Key certificate embedded within the PDF. View exactly who signed the document, their associated email, and the issuing Certificate Authority (CA).
Uploading unredacted legal contracts to a random cloud server is a massive compliance violation. This tool guarantees 100% privacy by parsing the file structure locally via your browser's memory.
In the modern enterprise, printing a contract, signing it with a pen, and scanning it back into a computer is obsolete. However, if you simply paste a JPEG image of your signature onto a digital invoice, you are inviting catastrophic fraud. Anyone with Photoshop can delete the $1,000 total and type $10,000. To prevent document tampering, you must use mathematical Digital Signatures.
A true Digital Signature relies on Public Key Infrastructure (PKI). When you sign a PDF using software like Adobe Acrobat, the software doesn't just attach an image. It executes a complex mathematical operation on the entire file.
First, it calculates a unique "Hash" (a massive string of letters and numbers) representing the exact layout, text, and data of the contract at that exact millisecond. It then takes that Hash and securely encrypts it using your strictly guarded Private Key.
This encrypted Hash is physically embedded deep within the byte structure of the PDF file. This effectively creates an unbreakable, mathematical "wax seal" over the document. An online PDF signature checker is used to inspect this seal.
What happens if a hacker tries to modify the signed PDF?
Imagine the hacker opens the PDF and changes the invoice amount.
When you upload the tampered file to the verification tool, the engine recalculates the Hash of the new, altered document. It then unlocks the original, signed Hash embedded in the file. The tool compares the two Hashes. Because the hacker changed the text, the new Hash will be completely different. The engine instantly throws a critical "Signature Invalid / Document Modified" alert.
How do you know the person who signed the document is actually who they claim to be?