E-Invoicing in Portugal: What Every Small Business Must Do Before 2027

If your business sends invoices in Portugal, the rules around what counts as a valid electronic invoice are tightening — and the transition period that let everyone email plain PDFs is ending. The headline: unstructured PDFs are on their way out, structured e-invoices (the CIUS-PT format) are coming in, and qualified electronic signatures become a hard requirement for PDF invoices that want to keep counting as electronic.

One warning before anything else: these deadlines have moved before — more than once. Portugal has extended the PDF transition period repeatedly through successive State Budget laws. Everything in this article reflects the situation at the time of writing (mid-2026). Before you spend money or change processes, confirm the current dates with the Portuguese Tax Authority (AT) and your accountant.

What is actually changing

Three separate things are converging, and they are often confused with each other:

1. The end of the "PDF counts as electronic" grace period. Since 2020, Portugal has allowed a plain PDF sent by email to be treated as a legal electronic invoice, as a temporary measure. That grace period has been extended year after year. When it finally lapses, a PDF invoice will only qualify as an electronic invoice if it carries a qualified electronic signature or seal — a cryptographic signature issued by a certified trust provider, not a scanned image of a handwritten one.

2. Structured e-invoicing for public-sector suppliers (B2G). If you sell to the Portuguese State — ministries, municipalities, public hospitals, schools — you are required to issue invoices in the CIUS-PT format: a structured XML document based on the European standard EN 16931, delivered through a certified channel, not a PDF attachment. Large companies have been covered since 2021; the obligation for micro, small and medium enterprises has been phased in on a slower, much-postponed schedule.

3. The EU horizon (B2B). Under the EU's "VAT in the Digital Age" (ViDA) package, structured e-invoicing and digital reporting will progressively become the norm for cross-border B2B transactions, with member states empowered to mandate domestic B2B e-invoicing. Portugal has not yet fixed a domestic B2B mandate date, but the direction of travel is unambiguous. Businesses that treat 2026–2027 as preparation time will have a boring, cheap transition. Businesses that ignore it will have an expensive one.

PDF vs. structured e-invoice: know the difference

This distinction matters because vendors sell solutions to both problems, and they are not interchangeable.

	Plain PDF	Signed PDF	Structured e-invoice (CIUS-PT)
Human-readable	Yes	Yes	Not directly (XML)
Machine-readable	No	No	Yes
Qualified signature	No	Yes	Signature or certified transmission
Valid B2G invoice	No	No	Yes
Valid B2B e-invoice after transition	No	Yes (verify current rules)	Yes

A signed PDF keeps you legal for ordinary B2B invoicing. A structured CIUS-PT invoice is what public-sector clients require and what the whole market is drifting towards, because software can ingest it without a human retyping numbers.

What to ask your invoicing software vendor

Portugal already requires certified invoicing software (the AT-certified programs, ATCUD codes and QR codes on invoices). So most businesses have a vendor. The question is whether that vendor is ready for the next phase. Ask them, in writing:

1. Do you support CIUS-PT output today? Not "on the roadmap" — today. Ask for a sample XML.
2. How do you deliver B2G invoices? Via which platform or access point, and what does onboarding a new public client involve?
3. Do you apply a qualified electronic signature or seal to PDF invoices? Who is the trust service provider, and is it included in my plan or a paid add-on?
4. What happens to my archive? Electronic invoices must be stored in a way that guarantees integrity and legibility for the legal retention period (10 years in Portugal). Where is the archive, and can I export it if I leave?
5. What does compliance cost me per year? Get the number. Some vendors charge per signed document; at volume this adds up.

If the answers are vague, start evaluating alternatives now, while you have time. Migrating invoicing software in a panic in December is how businesses lose billing days.

Action checklist by company size

Freelancers and sole traders:

• Confirm your invoicing tool (or the AT's free Portal das Finanças invoicing) covers your case after the transition ends.
• If you email PDF invoices, find out when your tool will sign them — or whether you should invoice through a platform that handles it.
• Ask your accountant once, this quarter, and put a reminder to re-check each State Budget season (October–December), because that is when deadlines move.

Small companies (2–20 people):

• Everything above, plus: inventory every system that creates invoices (POS, e-commerce store, ERP, subscription billing). Each one needs a compliance path.
• If you sell to any public entity, treat CIUS-PT as urgent, not future — the B2G obligation is the one already in force for larger suppliers and phasing in for smaller ones.
• Budget for it. Realistic range: €0–30/month extra on a modern SaaS invoicing plan, more if you need custom integration work.

Companies with custom systems:

• If your website, store or internal app generates invoices through an API (Moloni, InvoiceXpress, Vendus, KeyInvoice and similar), verify the API supports structured output and signed documents, and that your integration passes the right fields — buyer VAT numbers, ATCUD, document types.
• If invoicing is stitched together with manual steps, this is the moment to automate: the compliance change and the efficiency win share the same project.

The honest cost picture

For most small businesses, complying is cheap: modern Portuguese invoicing SaaS runs roughly €5–30/month and the serious vendors are building CIUS-PT and qualified seals into their plans. The expensive scenario is custom: if your e-commerce site or internal tool creates invoices its own way, integration work is typically a few days of development — far less than rebuilding under deadline pressure. If the change pushes you to modernise a wider system, check whether your project qualifies for public co-financing for SME digitalisation (in Portugal, vouchers have covered up to 75% of eligible costs — verify current programmes on portugal2030.pt).

And to repeat the only advice in this article that is guaranteed not to expire: confirm the current deadlines with the AT and your accountant before acting. They have moved before. They may move again. The businesses that get hurt are not the ones that prepared early — they are the ones that assumed the next extension.

If your invoicing depends on a website, store or custom system that needs to be brought up to date, tell us what you have and we'll estimate the work in 24 hours.