How to sign a document with a digital certificate

A digital certificate is like an ID card on your computer: it identifies its holder and lets them sign documents with a signature the law treats as advanced or qualified. Here’s how to get one and use it.

MultiDocs team2 min readUpdated 29 October 2026With official sources

In 30 seconds

  • The FNMT digital certificate is free and is used for signing and dealing with government services.
  • A qualified certificate lasts five years at most and has to be renewed.
  • With a certificate you create a qualified or advanced signature; for everyday use you don’t always need one.

What a digital certificate is

It’s a file, issued by a trust service provider, that links your identity to a set of keys for signing. The most common one for individuals in Spain is the personal certificate from the FNMT (Fábrica Nacional de Moneda y Timbre, the Spanish Royal Mint). The electronic ID card (DNIe) also carries signing certificates.

Official figures

5 years

is the maximum a qualified certificate lasts in Spain.

Source: BOE, Ley 6/2020 art. 4.2
80.7%

of people aged 16 to 74 dealt with government services online in the last year.

Source: INE, 2025
38.1%

filed their income tax return online in the last year.

Source: INE, 2025

How to get the FNMT certificate

  1. Apply for it on the FNMT’s online portal. You’ll get an application code by email.
  2. Prove your identity with that code at a registration office (for example, the Tax Agency or Social Security) or by the remote methods the FNMT offers.
  3. Download it on the same computer and browser you applied from.

The exact steps and requirements may change: always check the FNMT’s official portal.

Signing a document with the certificate

The most common way is AutoFirma, the Spanish government’s free app. You can also sign PDFs with Adobe Acrobat Reader, using the certificates option.

Do I need it to sign anything?

No. The certificate is essential when a procedure requires it (many with government bodies). For a quote, a consent form or a contract between individuals or with your company, an electronic signature with a certificate of completion, like MultiDocs’, is valid and much simpler, especially if the signer doesn’t have a digital certificate.

FAQs

How much does the FNMT certificate cost?

The FNMT personal certificate for citizens is free.

How long does the certificate last?

It’s valid for a limited time (several years) and has to be renewed before it expires. The date is shown on the certificate itself.

Is a digital certificate the same as a digital signature?

The certificate is the tool; the digital signature is what you do with it on a document.

Official sources

We checked each source on 29 October 2026. If you spot outdated information, write to us at info@multidocs.es.

More guides

Signing with a certificateHow to sign a PDF with AutoFirmaSign a PDF with your digital certificate or DNIe.Signing with a certificateHow to sign a document with the electronic ID cardCard reader, PIN and AutoFirma, step by step.Signing with a certificateHow to sign documents with Cl@veFor dealing with government services.