X.509 PDF Digital Signer
Cryptographically sign PDF documents using your .p12 or .pfx certificate. 100% private, runs locally in your browser without uploading sensitive files.
X.509 PDF Digital Signer
Cryptographically seal your PDF with a .p12 or .pfx certificate. 100% private.
Why use an X.509 Digital Signature?
If you draw your signature on a PDF, anyone can copy that image, paste it onto another document, or modify the text after you've signed it. It offers visual proof, but no legal or cryptographic security.
An X.509 Digital Signature solves this. It uses public-key cryptography to create a unique digital fingerprint of the document. If even a single pixel is changed after signing, Adobe Acrobat and other PDF readers will flag the document as altered.
ToolDeck processes everything locally using WebAssembly. This means your private key and your certificate password never leave your browser. It is the most secure way to sign contracts, tax forms, and legal documents online for free.
How it works
- 1
Upload PDF
Select the PDF document you want to digitally sign.
- 2
Add Certificate
Provide your .p12 or .pfx certificate file and enter the password.
- 3
Download Signed
The browser will cryptographically seal the document. It is now legally binding.
Frequently Asked Questions
What is an X.509 digital signature?
An X.509 digital signature is a cryptographic method used to verify the authenticity and integrity of a document. It uses a digital certificate (.p12 or .pfx) issued by a Certificate Authority (CA) to prove the document was signed by you and has not been altered since.
How is this different from the normal Sign PDF tool?
The normal Sign PDF tool allows you to draw a visual signature, which is essentially an image placed on the PDF. An X.509 digital signature embeds cryptographic data into the file structure. If someone changes even a single pixel after signing, Adobe Acrobat will show a red warning that the document is invalid.
Is it safe to upload my certificate here?
We do not upload your certificate! The signing process happens entirely inside your browser. Your private key and password never touch our servers. This is 100% private.
Where do I get a .p12 or .pfx certificate?
You can purchase one from trusted Certificate Authorities (like SSL.com, Sectigo, or GlobalSign). Some companies also issue their own internal certificates for employees.
Will Adobe Acrobat show a green checkmark?
Yes, if the certificate is trusted by your computer. When you open the signed PDF in Adobe Acrobat, you will see a signature panel that validates the integrity of the document.
What if I forget my certificate password?
There is no way to recover the password of a .p12 file. If you lose it, you cannot use that certificate. You will need to request a new certificate.