Digital certificates: why they work… until they don’t

06 Apr 2026

Updated: May 2026

These days, the digital certificate has become essential. From accessing the Tax Agency to signing documents without leaving home, everything goes through that small file that, in theory, "just needs a double-click to install."

The problem is that, even though it sounds simple, that's exactly where most digital certificate issues start — problems that the average user has no idea how to handle.

"I installed it years ago and it worked fine…"

This is the most common story. One day you installed it, it worked perfectly… and you never touched it again.

Until one day:

It doesn't appear in the browser
It won't let you sign documents
The Tax Agency doesn't recognise it
Or the certificate has simply disappeared

And the worst part: you don't know where it is or how you installed it.

The big mistake: installing without understanding

When you install a digital certificate (like those from the FNMT), the system asks you several questions.

One of them — a critical one — usually goes unnoticed: 👉 whether the certificate will be exportable or not

Most users just click "Next" without looking.

The consequence:

You can't copy it to another computer
You can't make a backup
And if the machine fails… you lose everything

Changing computers: the critical point

This is another classic.

You get a new computer and think: "I'll just copy the certificate across"

But it's not always that straightforward.

Depending on how it was originally installed:

It may not appear in the correct certificate store
It may not be exportable
It may ask for passwords you no longer remember
It may be tied to the old system

And it's precisely in these — situations where the certificate stops working — that most users end up completely stuck.

Browsers, systems and compatibility

Another common problem: the certificate "is there," but it doesn't work.

Because:

Each browser handles certificates differently
Windows, macOS and browsers aren't always aligned
Some settings change without warning after updates

Result: 👉 the certificate exists… but you can't use it

Signing PDFs: when everything fails at the last step

This is usually the most frustrating scenario.

Everything seems fine until:

The PDF doesn't detect the certificate
The signing software fails
Or an unexplained error appears

And of course, you need to sign something urgently.

Common problems in 2026

These are the cases we're seeing most frequently this year:

Chrome and older certificates Chrome 124 onwards dropped support for certain certificates using legacy SHA-1 algorithms. If your certificate is from before 2020 and stopped working this year without you changing anything, this is likely the reason. The fix isn't to reinstall the certificate — it's to renew it through the FNMT and get a new one.

FNMT renewal that gets stuck loading The FNMT electronic office updated its renewal system. If you try to renew and the page keeps loading indefinitely, the problem is usually old browser cache or outdated site cookies. Try in incognito mode or with your browsing history cleared before calling anyone.

AutoFirma and updated Windows 11 AutoFirma 1.8 (the current version) has known compatibility issues with Windows 11 24H2, the major update from late 2024. If you updated Windows recently and AutoFirma stopped working or crashes on its own, there's a specific patch available on the Ministry's website. Simply reinstalling AutoFirma is not enough — you need to apply the correct patch for your version of Windows.

Frequently asked questions

Why does my digital certificate work in Edge but not in Chrome? Chrome uses its own certificate store in some versions of Windows, while Edge uses the system store. If it works in one browser but not the other, the certificate is installed in the wrong store, or it needs to be imported into the one Chrome uses. It's not a problem with the certificate itself — it's about where it's stored.

Can I have the certificate installed on two computers at the same time? Yes, as long as you exported it as a .p12 (or .pfx) file with a password when you originally installed it. If you didn't do that at the time, it's no longer possible to export it — you'd need to request a new one from the FNMT. This is why it's important to export it correctly right after installing it.

What do I do if the certificate shows as expired even though I just renewed it? The browser may still be showing the old version of the certificate from cache. You need to manually delete the old certificate from the store before installing the new one. If both exist at the same time, the system doesn't know which one to use and may pick the expired one.

Why does it say "invalid certificate" on the electronic office if it looks correct on my PC? It may be that the site doesn't recognise the complete certificate chain. Some certificates require the FNMT root certificates to also be installed. If those intermediate certificates are missing, validation fails even if your personal certificate is perfectly fine.