What Is a Digital Signature? Definition and How to Create One

When you sign a contract online by typing your name, you might think you’ve created a digital signature — but true digital signatures use cryptography and digital certificates to be legally binding. This article breaks down what a digital signature really means, how it works, and how you can create one yourself, referencing standards from NIST and the EU’s eIDAS regulation.

Countries recognizing digital signatures: Over 60 nations have laws validating digital signatures (e.g., eIDAS in EU, ESIGN in US). · Core cryptographic mechanism: Public key infrastructure (PKI) with paired private and public keys. · Legal equivalence: Digital signatures carry the same legal weight as handwritten signatures in most jurisdictions.

The table below summarizes key attributes of digital signatures.

What is a Digital Signature?

A digital signature is an electronic, encrypted stamp of authentication that confirms the signer’s identity and ensures the document has not been tampered with. As Adobe Help Center (PDF certification guide) describes, it relies on a mathematical scheme where a private key creates the signature and a public key verifies it.

How digital signatures work (public key cryptography)

• The signer uses a private key to encrypt a hash of the document. The recipient uses the signer’s public key to decrypt and compare hashes (NIST FIPS 186-5).
• This process is enabled by Public Key Infrastructure (PKI), which supports creation, distribution, and revocation of digital certificates (CISA (U.S. cybersecurity agency)).
• A digital certificate, issued by a Certificate Authority (CA), binds the public key to the signer’s identity (Cloudflare Learning Center).

Digital signature vs. electronic signature

Two terms, one key difference: security and legal standing. The table below lays out the contrast.

Three dimensions, one pattern: electronic signatures are a broad legal category, while digital signatures are a specific technical subset that uses encryption.

The implication: for contracts, tax filings, and anything that could go to court, insist on a digital signature. For low-risk agreements, an electronic signature may suffice.

What Does a Digital Signature Look Like? Examples

If you’ve ever seen a signed PDF with a blue ribbon or a green checkmark badge, you’ve already seen a digital signature. It’s not just a squiggly line — it’s a visual seal that includes metadata about the signer and the certificate.

Visible signature marks on documents

• In Adobe Acrobat, a valid digital signature appears as a signed seal with a certificate icon (Adobe Help Center).
• DocuSign displays a signature badge with a green checkmark when a valid certificate is used.
• Microsoft Office shows a blue ribbon in the signature line for digitally signed documents.

Examples of signed PDFs and emails

• Signed contracts: A PDF with a certification signature indicates the document has not been altered after signing.
• Email authentication: S/MIME signatures in emails use digital certificates to prove the sender’s identity.
• Software code signing: Developers sign executables so users can verify the publisher.

The pattern: visual signature badges provide a quick way to verify authenticity, but always check the certificate details.

How to Create a Digital Signature

Creating a digital signature requires a digital certificate and a tool that supports signing — typically a PDF reader like Adobe Acrobat or an online service like DocuSign. The process is more involved than typing your name, but it’s still manageable.

Using Adobe Acrobat to sign a PDF

1. Open the PDF in Adobe Acrobat and click on the Fill & Sign or Certificates tool.
2. Select Digitally Sign and drag a rectangle where you want the signature to appear.
3. Choose a Digital ID (your certificate) from the list, or create a new self-signed digital ID if you don’t have one from a CA (Adobe Help Center (certification workflow)).
4. Set a password for your digital ID (if creating locally) and click Sign. Adobe recommends removing JavaScripts or embedded media before certifying a PDF.
5. Save the signed PDF. The signature badge will appear with details of the signer and certificate.

Creating a signature with DocuSign or other e-signature tools

• Upload your document to DocuSign and choose Sign. The service will guide you to add a signature field and select a digital certificate if you have one.
• Some tools offer a basic electronic signature for free but require a paid tier for true digital signatures with certificates.

Generating a self-signed digital certificate for testing

On Windows, you can create a self-signed certificate via Internet Options → Content → Certificates (Microsoft Q&A guidance). In Adobe Acrobat, you can generate a self-signed digital ID stored as a PKCS#12 file (Cornell Finance (university guide)).

The bottom line: Always use a trusted certificate from a recognized CA for legally binding documents.

How to Obtain a Digital Signature (Including Free Options)

Getting your own digital signature means acquiring a digital certificate from a trusted Certificate Authority — or, for limited use, using a free tool that creates a certificate automatically.

Purchasing a digital certificate from a CA

• Major CAs include DigiCert, GlobalSign, Let’s Encrypt (free for servers), and Adobe Certified Trust Services. Prices range from $20/year for basic email certificates to $200+ for qualified signatures.
• India’s licensed CAs (under CCA) issue digital signature certificates for e-filing and e-tendering (Controller of Certifying Authorities, India).

Free digital signature services (limitations and use cases)

• Canva and SmallPDF offer signature generators that create electronic images — not true digital signatures with certificates (Canva signature generator).
• Adobe offers a 30-day trial of its certificate service for testing.
• For open-source testing, use OpenSSL to create a self-signed certificate.

Why this matters: A free online tool may produce a “signature” that looks the part but holds no legal weight. For contracts, taxes, or compliance, spend the money on a proper certificate.

How to Check if a Digital Signature Exists

Verifying a digital signature is often as simple as opening a signed PDF in a reader. The software checks the certificate’s validity and trust chain automatically.

Verifying signatures in PDF readers

• In Adobe Acrobat, the signature panel lists the signer, certificate issuer, and validity status. A green checkmark means valid; a red X means a problem.
• Microsoft Edge or Chrome also validate signatures when viewing PDFs — look for a badge in the toolbar.

Checking certificate validity and trust status

• Double-click the signature to open the certificate properties. Check the issuance date, expiration date, and whether the certificate was revoked by the CA.
• Valid signatures display a blue ribbon or green checkmark.
• Invalid or untrusted signatures show warnings such as “Certificate is expired” or “Document has been altered.”

The trade-off: even a valid signature only proves integrity up to the moment of signing. After the certificate expires, long-term validation may require additional time-stamping services.

The summary: Confirmed facts are backed by standards bodies; unclear areas require further regulatory evolution.

Expert Perspectives on Digital Signatures

“A digital signature is an electronic, encrypted stamp of authentication on digital information.”

— Microsoft Support (definition of digital signature)

“A digital signature is a mathematical scheme for verifying the authenticity and integrity of digital messages or documents.”

— Wikipedia (Digital signature)

“Digital signatures can help ensure integrity, authenticity, and non-repudiation in electronic transactions.”

— GSA (U.S. General Services Administration)

Summary: Digital signatures are not a marketing gimmick — they are a cryptographic standard backed by governments and standards bodies worldwide. For anyone handling sensitive documents, the choice is clear: invest in a legitimate digital certificate, or risk relying on a visual placeholder that offers no real protection. For the average user, using a free online tool to “sign” a PDF is fine for casual correspondence, but when legal validity matters, only a true digital signature from a trusted CA will hold up in court.

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