The short answer: a digital signature uses cryptography to prove who signed a document and that it hasn't been altered since. OpenSign™ lets you apply a free digital signature online, backed by a tamper-evident audit trail and certificate of completion — and because it's open source, you can verify exactly how it works.
Digital signature vs electronic signature
An electronic signature shows intent to sign. A digital signature is the underlying technology — a cryptographic mechanism that binds the signature to the document so any later tampering is detectable. Every OpenSign signature is protected this way and recorded in an audit trail.
How to add a free digital signature
- Create a free account at OpenSign.
- Upload your PDF or document.
- Add a signature field and sign by drawing, typing or uploading.
- Finish to seal the document with a tamper-evident record.
- Download the signed file and its certificate of completion.
What makes a digital signature secure
- Integrity — any change after signing invalidates the document seal.
- Authentication — the audit trail records signer identity, time and IP.
- Non-repudiation — signers cannot credibly deny they signed.
- Encryption — sensitive documents are protected in transit and at rest.
Why choose OpenSign
OpenSign is free, open source and self-hostable, so you get bank-grade signing security without a subscription or vendor lock-in. For developers, the same capabilities are available through the eSignature API.
Ready to try it? Create a free OpenSign account and start signing documents in minutes — no credit card required. Prefer to run it yourself? OpenSign is 100% open source on GitHub.