Are electronic signatures legal in Mexico? Código de Comercio, NOM-151 and e.firma

In Mexico most people first meet electronic signatures through the SAT: the e.firma you need to file taxes or issue invoices. Then a landlord, employer or supplier sends a contract through an e-signature platform and the question comes up. is that as valid as signing on paper, and does it need NOM-151?

The answer depends on whether the document is a commercial or civil contract, a dealing with the federal government, or an act that must pass through a notary. This guide covers each.

The short answer

• Electronic signatures are legally valid in Mexico. A reform published in 2000 amended the Código de Comercio, the Código Civil Federal and the Federal Code of Civil Procedure to recognise data messages (mensajes de datos). A 2003 reform added detailed rules on firma electrónica, firma electrónica avanzada o fiable and certification service providers.
• An advanced or reliable electronic signature meets the law's requirements for a signature and has the same effect as a handwritten one. A simple electronic signature is also valid, but its weight as evidence depends on how well you can show who signed.
• NOM-151-SCFI-2016 sets how data messages must be preserved so their integrity can be proven, through a constancia de conservación from an accredited provider. It strengthens evidence; it is not what makes a signature valid.
• For dealings with the federal public sector, the Ley de Firma Electrónica Avanzada (2012) applies, and the SAT e.firma is the certificate most people use. Tax matters have their own rules in the Código Fiscal de la Federación.
• Acts that must be in a public deed: such as most sales of real estate. Still need a notary.

The law

Código de Comercio

The electronic commerce rules are in the Código de Comercio, Book Two, Title Two, "Del Comercio Electrónico" (articles 89 to 114). They define:

• Firma electrónica: data in electronic form attached to or logically associated with a data message, used to identify the signer and show their approval of the information.
• Firma electrónica avanzada o fiable: an electronic signature that meets the requirements of article 97: the creation data belong exclusively to the signer, were under the signer's exclusive control at signing, and any later alteration of the signature or of the message can be detected.
• Prestador de servicios de certificación (PSC): a provider accredited by the Secretaría de Economía to issue certificates, time-stamps and conservation records. Notaries and public brokers (corredores públicos) are among those who can be accredited.

Where the law requires a signature, a data message meets it if an electronic signature is used, and an advanced or reliable signature is presumed to meet the test. Because commercial law in Mexico is federal, these rules apply to commercial contracts throughout the country.

Código Civil Federal

The 2000 reform added article 1834 bis to the Código Civil Federal. Where a contract must be in writing and signed, that requirement can be met by electronic, optical or other technological means, as long as the information is attributable to the parties and accessible for later consultation. Where the law requires a public instrument before a notary, the notary and the parties may use electronic means to send and receive the terms, and the notary must record in the instrument how the information is attributed to the parties and keep a full copy. Each state has its own civil code for civil (non-commercial) matters, and most contain similar rules.

NOM-151-SCFI-2016

NOM-151-SCFI-2016, issued by the Secretaría de Economía, sets requirements for preserving data messages and digitising documents. A PSC issues a constancia de conservación: a time-stamped record, tied to a hash of the document, proving that the file existed in that exact form at that moment. Many Mexican e-signature platforms attach one to every signed contract.

It helps to be clear about what NOM-151 does and does not do. It proves integrity and date over time, which matters when the other side says a contract was changed or back-dated. It is not a condition for an electronic signature to be valid in general, although some institutions expect it and some specific rules require it. For example, electronic credit instruments such as a digital pagaré (see below).

Ley de Firma Electrónica Avanzada (2012)

The Ley de Firma Electrónica Avanzada, published in 2012, governs advanced electronic signatures used by the federal public administration and by individuals and companies dealing with it. Under article 7, electronic documents and data messages with an advanced electronic signature have the same effects as documents with a handwritten signature. The SAT is one of the law's certifying authorities, which is why the e.firma is accepted across federal procedures. Under article 4, the law does not apply to acts where using an advanced electronic signature is not feasible by law, nor to tax, customs and financial matters, which have their own rules. For commercial acts, the Código de Comercio governs.

Documents that need a notary or special treatment

Real estate and notaries

Transfers of real estate above low statutory thresholds must be in an escritura pública executed before a notario público and registered in the state's public property registry. Notaries increasingly use electronic tools, and article 1834 bis lets the parties exchange the terms electronically, but the act itself remains a notarial one governed by each state's notarial law. A preliminary promesa de compraventa is a private contract and can generally be e-signed. See Can you e-sign a property deed or sale contract?.

Digital pagarés

For years it was unclear whether a pagaré could exist only in electronic form. A reform to the Ley General de Títulos y Operaciones de Crédito, published in March 2024, settled it: credit instruments, including pagarés, can be issued electronically. The instrument needs an electronic signature attributable to the person signing it, it must be issued and kept through an information system that follows the Código de Comercio's rules on data messages and NOM-151, and a PSC must issue a conservation certificate for it. A PDF with a drawn signature, sent by email, does not meet those conditions. If you lend or sell on credit, use a platform built for electronic pagarés and take advice.

Employment contracts

The Ley Federal del Trabajo requires working conditions to be set out in writing, but it does not demand ink. Its 2012 reform added rules on digital documents and electronic signatures as evidence in labour proceedings (articles 836-A to 836-D). They tell the tribunal to weigh how reliable the method of creating and keeping the document was, whether the person it is attributed to can be identified, and whether it has stayed intact, with an expert check where needed. Telework, regulated since 2021, also requires a written contract. Employers commonly sign contracts electronically; for strongest proof, use an advanced signature or a platform that preserves the file with a NOM-151 constancia. See Can an employment contract be signed electronically?.

The SAT e.firma

The e.firma (formerly FIEL) is a certificate issued by the Servicio de Administración Tributaria (SAT) after an in-person identity check. It is used for tax filings, invoicing and many other federal procedures, and it meets the requirements of an advanced electronic signature. Businesses and platforms increasingly use it to sign private contracts as well.

It comes as two files and a password:

• a .cer file. The public certificate;
• a .key file. The encrypted private key;
• the private key password you chose.

It is valid for four years. The first e.firma requires an appointment at a SAT office; after that it can usually be renewed online while it is still valid or within a year of expiring. If it expired more than a year ago, you go back to a SAT office.

Can I use my e.firma in KovaPDF?

Not directly. KovaPDF's Digital Signature, like most PDF signing software, expects a single .pfx / .p12 file that bundles the certificate and private key. The e.firma is not issued in that format.

The two files can be combined into a .pfx using standard tools such as OpenSSL: the private key is decrypted with your password and packaged together with the certificate into a new password-protected .pfx. If you do this:

• Do it on your own computer: never upload your .key file and password to a converter website.
• Protect the new .pfx with a strong password; anyone with it can sign as you.
• Check that the receiving party accepts it. A PDF signed this way carries your SAT certificate, but many PDF readers do not trust the SAT's certificate chain by default, and a counterparty or authority may prefer the signature made in their own system or on the SAT's portal. The SAT also sets terms for the use of the e.firma, so review them.

For filings with the SAT and other agencies, use their own portals, which accept the .cer and .key files directly.

Where KovaPDF fits

• Commercial contracts, leases, service agreements, HR documents: Request Signatures. Add each signer, choose the order, place fields and optionally set an access code. Signers use a private link and need no account. Everyone gets the signed PDF with a certificate of completion (names, emails, open and sign times, IP addresses and browsers, document fingerprint), and the file is sealed with a trusted timestamp from an independent authority. That is a simple electronic signature with strong evidence. not a firma electrónica avanzada and not a NOM-151 constancia issued by an accredited Mexican PSC.
• A certificate as a .pfx file, including an e.firma you have combined yourself. Digital Signature creates a PAdES signature with a trusted timestamp.
• Your own signature on a form: Sign PDF.
• Checking a signed PDF: Verify PDF Signature.

KovaPDF cannot replace a notary, issue a NOM-151 constancia, or file with the SAT.