A digital signature is the cryptographic, certificate-based signature that paid PDF suites usually lock behind a subscription. PDF-Atlas does it for free, entirely in your browser: it embeds a PKCS#7/PAdES signature into the PDF using your certificate, making the document tamper-evident and independently verifiable. Your document and your private key never leave your device. No certificate? Generate a self-signed one in seconds, right here.
Digitally Sign PDF in a few steps
- 1
Open the PDF you want to sign.
- 2
Provide a PKCS#12 (.p12/.pfx) certificate and its passphrase — or generate a self-signed certificate on the spot.
- 3
Add optional details like reason and location.
- 4
Sign, and download the cryptographically signed PDF. Verify it anytime with the Validate Signature tool.
What Digitally Sign PDF is good for
Tamper-evident documents
Guarantee that a contract, invoice, or report cannot be altered after signing without detection.
Verifiable identity
With a certificate from a trusted authority, recipients can confirm exactly who signed the document.
Privacy-critical signing
Sign sensitive documents without ever uploading them or your private key to a third-party service.
Frequently asked questions
- Do I need a certificate to use this?
- You can use an existing PKCS#12 (.p12/.pfx) certificate, or generate a self-signed certificate directly in the tool. A self-signed certificate still makes the document tamper-evident; it just is not backed by a trusted authority, so validators will show "identity not verified".
- Is the signing really done in my browser?
- Yes. The cryptographic signature is produced locally with WebAssembly/JavaScript (node-forge). Your PDF and private key are never transmitted. You can read the source on GitHub.
- What about trusted timestamps?
- Trusted timestamps (RFC 3161) and revocation checks require contacting an external authority, which browsers block directly. PDF-Atlas routes only a hash — never your document — through a tiny same-origin proxy for those optional steps. The core signature works fully offline without them.
- How do I verify a signed PDF?
- Use the Validate Signature tool, or open the PDF in a reader like Adobe Acrobat, which will show the signature panel and validation status.
- Is Digitally Sign PDF free to use?
- Yes. Digitally Sign PDF is completely free, with no sign-up, watermarks, daily quotas, or file-size caps. You can process as many files as your device can handle.
- Are my files uploaded to a server?
- No. Digitally Sign PDF runs entirely in your browser using WebAssembly. Your documents never leave your device — there are no uploads, no servers, and nothing is stored or logged. That is what makes PDF-Atlas private by architecture.
- Does Digitally Sign PDF work offline?
- Yes. After the page has loaded once, the tool keeps working without an internet connection. You can also install PDF-Atlas as a desktop app or PWA for a fully offline experience.
- Is my data safe?
- Because all processing happens locally on your machine, your files are as safe as the device they sit on. Nothing is transmitted to PDF-Atlas or any third party.