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

06 Apr 2026

Updated: May 2026

Nowadays, 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 to be installed with a double click."

The problem is that, although it seems simple, that's where many problems with digital certificates that most users don't know how to manage.

"I installed it years ago and it worked…"

That's the most common thing. 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 recognize 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 FNMT), the system asks you several questions.

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

Most users simply click "Next" without looking.

Consequence:

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

Changing computers: the critical point

This is another classic.

You buy a new computer and think: "I'll copy the certificate and that's it"

But it's not always that simple.

Depending on how it was installed back then:

It may not appear in the correct 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 when most users get completely stuck.

Browsers, systems, and compatibility

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

Because:

Each browser manages certificates differently
Windows, macOS, and browsers aren't always aligned
Some configurations change without notice after updates

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

Signing PDFs: when everything fails at the last step

This point is usually the most frustrating.

Everything seems correct until:

The PDF doesn't detect the certificate
The signing program fails
Or an error appears without clear explanation

And of course, you need to sign something urgently.

Frequent problems in 2026

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

Chrome and old certificates Chrome 124 onwards removed support for certain certificates with legacy SHA-1 algorithms. If your certificate is from before 2020 and stopped working this year without you having touched anything, this is probably the reason. The solution isn't to reinstall the certificate — it's to renew it from FNMT with a new certificate.

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

AutoFirma and updated Windows 11 AutoFirma 1.8 (the current version) has known incompatibilities with Windows 11 24H2, the big update from late 2024. If you recently updated Windows and AutoFirma stopped working or closes on its own, there's a specific patch available on the Ministry's website. It's not enough to reinstall AutoFirma — you have to apply the correct patch according to your Windows version.

Frequently asked questions

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

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 at the time. If you didn't do it when you installed it, it's no longer possible to export it — you'd have to request a new one from FNMT. That's why it's important to export it properly right after installing it.

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

Why does it say "invalid certificate" on the electronic headquarters if it looks correct on my PC? It could be that the headquarters doesn't recognize the full certification chain. Some certificates also require the FNMT root certificates to be installed. If those intermediate certificates are missing, validation fails even though your personal certificate is fine.