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Electronic Signature PDF — Digital Sign with Certificate

Create PAdES B-B signatures with an X.509 cert (.p12/.pfx) or Autofirma. Validation depends on certificate validity and verifier trust settings; software cert material is handled locally.

  • Sign with a software X.509 certificate (.p12 / .pfx) or with Autofirma / DNIe / smartcard
  • Create a PAdES B-B signature; acceptance depends on the certificate and verifier
  • Software certificate material is handled locally; optional chain or timestamp services may use network

Digital signatures cryptographically bind certificate material to a document through a CMS/PKCS#7 envelope. OpenPDF creates PAdES B-B signatures using a software X.509 certificate (.p12 / .pfx) or Autofirma for a smartcard, DNIe or installed certificate. Acceptance depends on certificate validity and the verifier's trust settings; chain retrieval or optional timestamping can require the network.

How it works

  1. Open your PDF. Drop the document you need to sign onto OpenPDF.
  2. Choose your signing method. Use a compatible software certificate (.p12 / .pfx) or launch Autofirma to sign with a smartcard, DNIe, or a certificate already installed on your machine.
  3. Sign the document. For software certificates, enter your password and the signature happens locally in your browser — the cert never leaves your device. For Autofirma, pick the certificate in the native dialog and authenticate.
  4. Download the signed PDF. OpenPDF produces a PAdES-compliant PKCS#7 signature. Acceptance depends on the certificate, its validity and the verifier's trust settings; optional chain retrieval or timestamping may use the network.

Common use cases

  • Signing a Spanish administrative form (modelo, tax filing, INEM) with DNIe or FNMT certificate from the browser.
  • Preparing a PAdES signature for a government portal, then checking the certificate and portal requirements.
  • Signing a notarially-witnessed document with a software certificate (.p12/.pfx) without installing Autofirma.
  • Using a compatible smartcard or installed certificate through desktop AutoFirma; check the recipient’s requirements.

Frequently asked questions

Which certificate formats are supported?

Software X.509 certificates in PKCS#12 format (.p12 / .pfx) — accepted from FNMT, idCAT, ACCV, Camerfirma and any eIDAS-compliant issuer. Smartcards, DNIe and OS-installed certificates are supported through Autofirma.

Is the signature legally valid in Spain / the EU?

OpenPDF produces PAdES B-B signatures (ETSI EN 319 142). Whether a verifier accepts the result depends on the certificate, its validity and the verifier's trust settings; a qualified signature also requires the appropriate qualified certificate and device.

Does my certificate leave the device?

For software certificates, the password unwraps the certificate locally in the browser and the private key is not uploaded. Autofirma uses a local desktop bridge; certificate-chain retrieval or timestamping can still require the network.

Can I sign multiple documents in one session?

You can sign several PDFs while the certificate remains unlocked in that browser session. To stop using it, return to the signing-method selector and follow the tool's controls; persistent browser state is managed separately.

Why OpenPDF

OpenPDF is an independent project where PDF document processing runs in the browser using WebAssembly and modern JavaScript APIs. The toolkit includes merge, split, sign, organize, annotate, compress, watermark, page numbers, add image and fill forms. Practical limits depend on the operation, document and device. The page source and privacy policy describe consent controls, analytics, advertising and optional services before you use the tool with sensitive documents.

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