What is Digital Signature?

A cryptographic signature using public-key infrastructure (PKI) that mathematically proves authorship and detects any tampering.

A digital signature uses asymmetric cryptography, typically RSA or ECDSA, to bind a private key to a document. Anyone with the matching public key can verify (a) the signer's identity and (b) that the document hasn't changed since signing. Digital signatures are a subset of electronic signatures, distinguished by their cryptographic backing. Under eIDAS they're the basis of Advanced (AdES) and Qualified (QES) electronic signatures. PDF Verified hashes every signed document with SHA-256 and exposes the hash on a public verification URL so anyone can confirm authenticity.

Drop your document here and sign it now. PDF, Word and Excel all work: a .docx or .xlsx is laid out in your browser exactly as it was written, so there is nothing to convert first. Add a signature, a date, a company stamp or a watermark, then download it sealed. Free to start, no account, and the file is never uploaded to open it.

PKI and certificate authorities

Digital signatures rely on a Public Key Infrastructure (PKI): a trusted Certificate Authority (CA) issues a signing certificate after verifying the holder's identity. The signer's software uses the certificate's private key to encrypt a hash of the document; verifiers use the public key to decrypt and compare.

Hashes and tamper-evidence

Before signing, the document is hashed with SHA-256 (or stronger). Any change to a single byte produces a completely different hash, so a digital signature is also a tamper seal, if even one character changes after signing, verification fails.

When you need a true digital signature vs an eSignature

For most commercial contracts a captured eSignature is sufficient. For QES-grade transactions in regulated EU/UK contexts, or for cross-border filings that require non-repudiation, a TSP-issued digital signature is required. PDF Verified offers TSP integration on Business Plus.

What PDF Verified is, and what it is not

These checks are a screen, not a verdict. A clean result means nothing was found by the checks that were run, which is not the same as proof that a document is genuine, and a flagged result can have an innocent explanation such as a re-save or a scan. Read the findings rather than the headline, and where a decision carries real consequences, confirm the document with the party that issued it. It is a tool for examining a document, not for producing a forged or altered one.

PDF Verified is a tool for preparing, signing, stamping and checking documents. It is not a law firm, a compliance service or a forensic examiner, and nothing here is legal, financial or compliance advice. Requirements differ by country, by document type and by the party asking, so check what applies to your document before you rely on it, and take advice where the document matters. You are responsible for the documents you create, sign and send, and for having the authority to do so: signing or stamping in somebody else name, or as an organisation you do not represent, is forgery whatever tool is used. To the extent the law allows, we accept no liability for how a document made with this tool is used or relied on. The full position is in our terms of service.