Does my private key leave my device?

No. Signing runs entirely in your browser with node-forge and @signpdf. We never upload your key or PDF.

Why might signing fail?

Some PDFs with complex structure conflict with signature placeholders. Try printing to PDF first, or use a standard .p12 from your CA.

One file with -----BEGIN CERTIFICATE----- block(s) and a -----BEGIN PRIVATE KEY----- (or ENCRYPTED PRIVATE KEY) block. RSA keys are most widely tested.

Difference from Sign PDF?

This tool adds a PKCS#7 digital signature using your certificate. Sign PDF places a visual drawing or image without cryptographic signing.

Digital Signature PDF Online Free

Add a cryptographic digital signature to your PDF using X.509 certificates. Supports PKCS#12 (.pfx, .p12) and PEM formats. Your private key never leaves your browser. All processing happens in your browser. No uploads, no signup—your files never leave your device.

How to use

Upload PDF & certificate

Add your PDF, then your PKCS#12 (.pfx / .p12) or a combined PEM file (certificate + private key). Passwords are used only in your browser.

Unlock certificate

Click Unlock certificate. Check subject and validity. Optionally set reason, location, contact, and a visible signature box on the first page.

Sign & download

Sign PDF downloads a cryptographically signed file. Verify in Acrobat or another PDF reader. For drawn or image signatures without a certificate, use Sign PDF.

Frequently asked questions

Validate PDF Signature
Verify digital signatures in your PDF files. Check certificate validity, view signer details, and confirm document integrity. All processing happens in your browser.
Sign PDF
Add digital signatures to PDFs.
Flatten PDF
Make form fields and annotations non-editable.