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Electronic Signature PDF — Digital Sign with Certificate

PAdES B-B (ETSI EN 319 142) signatures with X.509 cert (.p12/.pfx: FNMT, idCAT, ACCV) or Autofirma for DNIe. Validated by Adobe Reader and EU eIDAS validators. Cert stays on-device.

Digital signatures are the administrative-grade alternative to a drawn mark — they cryptographically bind your identity to the document via a CMS envelope (PKCS#7, ~10-30 KB overhead) and remain validatable years later. OpenPDF produces PAdES B-B signatures (ETSI EN 319 142) using a software X.509 certificate (.p12 / .pfx from FNMT, idCAT, ACCV, Camerfirma, any eIDAS issuer) or Autofirma for smartcard, DNIe and OS-installed certificates. Validated by Adobe Reader and EU eIDAS validators; everything stays local to your device.

How it works

  1. Open your PDF. Drop the document you need to sign onto OpenPDF.
  2. Choose your signing method. Use a software certificate (.p12 / .pfx from FNMT, idCAT, ACCV, Camerfirma or any X.509 issuer) 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 that validates in Adobe Reader, valide.redsara.es (@firma) and EU eIDAS validators.

Common use cases

  • Signing a Spanish administrative form (modelo, tax filing, INEM) with DNIe or FNMT certificate from the browser.
  • Producing PAdES signatures that validate in @firma for submission to government portals.
  • Signing a notarially-witnessed document with a software certificate (.p12/.pfx) without installing Autofirma.
  • Using a smartcard or EU eIDAS certificate to sign procurement documents without native desktop tools.

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?

Yes. OpenPDF produces PAdES B-B signatures (ETSI EN 319 142) that validate in Adobe Reader, valide.redsara.es (@firma) and EU eIDAS validators. For qualified signatures, use a QSCD certificate.

Does my certificate leave the device?

No. Software certificates stay entirely in the browser — the password you enter is used to unwrap the certificate locally and the private key never leaves your device. Autofirma is a local desktop bridge, also offline.

Can I sign multiple documents in one session?

Yes. Once a certificate is unlocked in the browser, sign as many PDFs as you need. Close the tab to discard the unlocked certificate.

Why OpenPDF

OpenPDF is an independent project built around one principle: the PDFs you edit should never leave your device. Every tool — merge, split, sign, organize, annotate, compress, watermark, add page numbers — runs entirely in your browser using WebAssembly and modern JavaScript APIs. There is no upload step, no account, no email harvesting, and no premium tier gating the useful features. The codebase and the third-party scripts loaded for analytics and advertising are visible in the page source — Google AdSense and Google Analytics 4 load only after you accept cookies in the consent banner — so anyone can audit what is running before trusting the tool with sensitive contracts, scanned IDs, or financial documents.

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