Digital Sign PDF — Sign with an X.509 Certificate
Apply a PKI-based digital signature to your PDF using your own certificate and private key. Add signing details and a visible signature block, all processed locally in your browser.
Key Features
PKI Digital Signatures
Sign with your own certificate and private key using PKI cryptography, producing a verifiable PDF signature.
X.509 Certificate Support
Upload PFX/P12 or PEM certificates. Your certificate's subject, issuer, and validity are shown before signing.
Visible Signature Blocks
Add a visible signature with custom text or your own image, positioned anywhere on any page.
100% Private
Your certificate and document are processed entirely in your browser and never leave your device.
No Install, Free
Works on any device with a browser. No sign-up, no watermarks, and completely free.
What Is a PDF Digital Signature?
A digital signature uses a cryptographic certificate and private key to sign a PDF, creating a verifiable signature that proves who signed the document and that it has not been altered since signing. Unlike a drawn signature image, a digital signature is based on public-key infrastructure (PKI): the private key signs a digest of the document, and anyone can verify it with the corresponding public certificate. This tool signs the PDF with your own certificate, optionally adding a visible signature block with text or an image. Everything runs locally in your browser, so your private key never leaves your device.
How to Digitally Sign a PDF
Digitally signing a PDF takes just a few steps. Everything runs in your browser.
Upload your PDF
Drag and drop the PDF you want to sign, or click the upload area to select it.
Add your certificate
Upload a PFX/P12 or PEM certificate and enter its password. The certificate details are displayed for confirmation.
Set the signature options
Optionally add a reason, location, and contact, and enable a visible signature with text or an image.
Sign and download
Click Sign PDF and download the signed document. The signature can be verified by any PDF reader.
Good to Know
You need a certificate that contains a private key to sign — a certificate alone is not enough. Encrypted PDFs must be decrypted before signing. Your private key is used only locally in your browser and never transmitted. After signing, the document is locked against further changes without invalidating the signature. For legally binding signatures, use a certificate issued by a trusted certificate authority.