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Sign with a certificate

Add a cryptographic digital signature from your .p12 or .pfx certificate.

Runs in your browser. Your file is never uploaded.

Sign with a certificate in short

Add the finished PDF, then open your .p12 or .pfx certificate with its password, then sign and download the signed copy. It's free, there's no sign-up, and it runs in your browser, so the file never leaves your device.

How to use Sign with a certificate

  1. 1Add the finished PDF.
  2. 2Open your .p12 or .pfx certificate with its password.
  3. 3Sign and download the signed copy.

Good to know

  • Your certificate, its password and private key are used only in your browser. Nothing is uploaded.
  • The signature covers the whole file. Any later edit breaks it, so make all your changes first.
  • Whether a reader shows your identity as trusted depends on who issued your certificate. Self-signed certificates prove the file is unchanged but not who signed it.
  • RSA certificates are supported. Elliptic-curve certificates aren't yet.
  • A PDF that is already signed is left alone, because rewriting it would break the existing signature.
  • This adds the signature's own signing time, not a timestamp from a trusted time server.
  • This tool runs in your browser. Very large files depend on your device's memory.

Guides

  • How to sign a PDF

    Sign a PDF free in your browser, either by drawing your signature on the page or by adding a certificate-based digital signature. Which one you need, the steps for each, and what breaks a signature.

Sign with a certificate: common questions

Is Sign with a certificate free?
Yes. Sign with a certificate is free and works without an account, for files up to 25 MB and 150 pages. A free account raises that to 50 MB and 400 pages.
Are my files uploaded to a server?
No. Sign with a certificate runs in your web browser, so the file is read on your own device and never sent to ConvertFile.
What's the difference between this and Sign PDF?
Sign PDF places a picture of your handwritten signature on the page. This tool adds a cryptographic signature from a digital certificate, which PDF readers can check: it proves the file hasn't changed since signing and, with a certificate from a trusted issuer, who signed it.
Where do I get a certificate?
From a certificate authority, your employer or a government identity scheme, usually as a .p12 or .pfx file. You can also make a self-signed one, which proves the file is unchanged but not who you are.
Is my private key uploaded?
No. The certificate file is opened and used inside your browser. Neither it nor its password is sent to our servers.
Is this a legally binding signature?
That depends on your jurisdiction, the document and the certificate, not on this tool. We can't give legal advice. If it matters, check what the other party or the law requires.
Does Sign with a certificate work on Mac, Windows, Android and iPhone?
Yes. It runs in any modern web browser, with nothing to install. Very large files work best on a desktop or laptop, because in-browser tools use your device's memory.

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