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Firma digital

Firma criptográficamente un PDF con tu certificado P12/PFX (PAdES) — el certificado nunca sale de tu navegador. Firma visible opcional.

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A picture of a signature proves nothing: anyone can copy it from one document onto another. A digital signature is a different kind of object — a cryptographic operation with your private key that binds your identity to these exact bytes, so any later change to the document breaks it visibly. This tool signs a PDF in the PAdES form readers expect, using a certificate you already hold as a .p12 or .pfx file.

The certificate and its password are read inside your browser and never leave it, which is not a small claim for a private key. You can add a visible signature block on a page you choose, but the visible part is decoration: what carries the weight is the cryptography underneath. Only RSA keys are supported, and a certificate has to come from an authority somebody trusts — this signs with the identity you already have, it does not issue one.

How it works

  1. Drop in the PDF, and your .p12 or .pfx certificate.
  2. Unlock the certificate with its password — it is read locally.
  3. Optionally place a visible signature block on a page.
  4. Sign and download the signed PDF.

What people use it for

  • Signing a contract in a form the other party's software can verify.
  • Submitting a document to an administration that requires a digital signature.
  • Making a published document tamper-evident so alterations are detectable.

Frequently asked questions

Is my file uploaded to a server?
No. The file is opened by JavaScript and WebAssembly running inside your own browser tab. It is never uploaded, there is no server-side processing and nothing is stored — closing the tab discards everything.
Does my certificate leave the browser?
No. The .p12 and its password are read locally and used to sign in the page itself. Nothing about the certificate or the key is uploaded — which is the whole reason to sign here rather than on somebody's server.
Where do I get a certificate?
From a certification authority, often through your government, your chamber of commerce or a qualified provider. This tool signs with an identity you already hold; it cannot create or vouch for one.
It says my key type is not supported.
Only RSA keys are handled. Certificates issued with elliptic-curve keys will not sign here — check what your provider issued, or ask them for an RSA certificate.
Is a visible signature required?
No. The signature is valid whether or not anything is drawn on the page; readers show it in their signature panel either way. A visible block is useful when a human will look at a printout, since the cryptography is invisible on paper.

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