Electronic signature in Portugal: types, legal validity and framework
In Portugal, an electronically signed document is legally valid. Regulation (EU) No 910/2014 (eIDAS) establishes that an electronic signature cannot be denied legal effect solely because it is electronic, and Decreto-Lei n.º 290-D/99 governs electronic documents in national law. What varies between the different types of signature is not validity — it is evidential weight.
What types of electronic signature are there?
The eIDAS Regulation defines three levels of electronic signature, with increasing requirements for identifying the signatory and for the integrity of the document.
| Type | What it requires | Evidential weight |
|---|---|---|
| Simple | Electronic data attached to other data that the signatory uses to sign (for example, a drawn stroke or an acceptance click). | Freely assessed by the court. |
| Advanced | Uniquely identifies the signatory, is under their sole control and makes any later change to the document detectable. | Freely assessed, but with strong technical support. |
| Qualified | An advanced signature created by a qualified device and based on a qualified certificate issued by an accredited trust service provider. | Treated as a private document with recognised authorship (Article 376 of the Código Civil, the Portuguese Civil Code). |
What evidential value does an electronically signed document have?
An electronic document with a qualified electronic signature is treated as a private document with recognised authorship, under Article 376 of the Código Civil. It is the highest level an electronic signature can reach, and it is what you get when you sign with the Digital Mobile Key (Chave Móvel Digital, CMD) or the Citizen Card (Cartão de Cidadão).
By contrast, a document containing only scanned signatures — an image of a signature pasted into a PDF, for example — is subject, as evidence, to the court's free assessment. It can still be used as evidence, but it is up to the court to decide how much weight to give it.
This is why the choice of signature method matters: not to make the document valid, but to determine how hard it will be to challenge later.
Can contracts be concluded electronically?
Yes. A general principle of equivalence between paper and electronic documents applies, except where Portuguese law requires additional formalities — a public deed, an authenticated document or in-person certification of signatures.
The following, among others, still require special formalities:
- Transfer of real estate and creation of mortgages
- Incorporation of commercial companies (except under their own simplified regimes)
- Enforceable instruments that the law subjects to a special form
- Powers of attorney that require signature certification
- Loan agreements of more than €25,000
Which documents are commonly signed electronically?
In the vast majority of everyday business cases, there is no special form requirement and an electronic signature is enough.
- Employment contracts, addenda and non-disclosure agreements (NDAs)
- Service agreements and supplier contracts
- Commercial proposals and contract awards
- Lease agreements
- Declarations, authorisations and consents to data processing
- Invoices, statements, purchase orders and business correspondence
Can someone else apply my electronic signature?
No. The certificate behind a qualified signature is under the holder's sole control, and sharing your signature PIN amounts to sharing your legal identity.
What the law allows is representation: a director or manager can sign on behalf of the company within the powers granted to them, and can sub-delegate those powers by resolution of the board of directors. In that case the signature is still that of the person signing, acting on behalf of someone else.
Does my location matter when I sign?
The signatory's physical location at the time of signing is generally irrelevant to the validity of the act, and the same applies to the location of the server processing the signature. What matters is the law applicable to the contract and, where there is one, the jurisdiction agreed by the parties.
What server location does determine is the applicable data protection regime. AssinaJá stores documents and personal data in Portugal, within the European Union, in compliance with the GDPR.
Can a document combine several types of signature?
Yes. It is common and entirely acceptable for the same document to contain signatures of different levels — for example, one party signs with the Digital Mobile Key and the other with an advanced signature by OTP.
Each signature keeps its own evidential weight. The document is not "levelled down": what is assessed is the authorship of each signature individually.