Diagnostic

Electronic signatures and contract retention: when a signed PDF actually serves as proof

The Commercial Code recognizes electronic contracts. What gets litigated is whether the signing and retention method is reliable.

LEXURE Commercial Contracts Practice Team 7 min read Regulatory status verified in 2026

Many com­mer­cial con­tracts today are signed on a plat­form and saved in a shared folder, and that is valid. The prob­lem arises when the other party denies having signed or claims the doc­u­ment was altered, and the com­pany dis­cov­ers that all it has is a PDF with no way to prove who signed it or that it remains intact.

What the law requires

Elec­tronic con­tracts are bind­ing. Under Arti­cle 80 of the Com­mer­cial Code (Código de Com­er­cio), com­mer­cial con­tracts entered into by elec­tronic means are formed when the accep­tance is received. Infor­ma­tion may not be denied valid­ity or bind­ing force because it is con­tained in a data mes­sage, and data mes­sages are admis­si­ble evi­dence (Arti­cle 89 Bis). When the law requires writ­ten form, that require­ment is met by a data mes­sage that remains intact and acces­si­ble for later con­sul­ta­tion (Arti­cle 93).

Simple and advanced sig­na­tures. A simple elec­tronic sig­na­ture is any elec­tronic data asso­ci­ated with the mes­sage that iden­ti­fies the sig­na­tory and indi­cates that the sig­na­tory approves its con­tent (Arti­cle 89). An advanced or reli­able elec­tronic sig­na­ture is one that meets four con­di­tions: the cre­ation data cor­re­spond solely to the sig­na­tory, were under the sig­na­tory’s exclu­sive con­trol at the time of sign­ing, and it is pos­si­ble to detect any later alter­ation of both the sig­na­ture and the mes­sage (Arti­cle 97). The law does not require an advanced sig­na­ture for every­thing, since a sig­na­ture appro­pri­ate for the pur­poses of the mes­sage is suf­fi­cient (Arti­cle 97, first para­graph), although in lit­i­ga­tion the dif­fer­ence car­ries weight.

What the judge weighs. In assess­ing a data mes­sage, pri­mary con­sid­er­a­tion is given to the reli­a­bil­ity of the method by which it was gen­er­ated, archived, com­mu­ni­cated, or retained (Arti­cle 1298-A). That is why two con­tracts with the same con­tent can have very dif­fer­ent evi­den­tiary weight.

Reten­tion. Mer­chants must retain for at least ten years the data mes­sages that record con­tracts, and the infor­ma­tion must remain com­plete and unal­tered from the moment it was gen­er­ated in its final form (Arti­cle 49). The offi­cial stan­dard that sets the require­ments is NOM-151-SCFI-2016, pub­lished in the Offi­cial Gazette of the Fed­er­a­tion (DOF) on March 30, 2017, which pro­vides for reten­tion cer­tifi­cates with dig­i­tal time stamps issued by cer­ti­fi­ca­tion ser­vice providers accred­ited by the Min­istry of Econ­omy (Sec­re­taría de Economía). The cer­tifi­cate does not turn the doc­u­ment into con­clu­sive evi­dence, but it estab­lishes the reli­a­bil­ity of the reten­tion method, which is the point in dis­pute.

The SAT e.firma is not the com­mer­cial rule. The e.firma issued by the Tax Admin­is­tra­tion Ser­vice (SAT) is grounded in the Fed­eral Tax Code (Código Fiscal de la Fed­eración) for tax fil­ings (Arti­cle 17-D). It may be used in pri­vate con­tracts if the par­ties agree, but com­mer­cial trans­ac­tions are gov­erned by the Com­mer­cial Code.

A pro­ce­dural change under­way. Under an amend­ment pub­lished on Novem­ber 14, 2025, the National Code of Civil and Family Pro­ce­dure (Código Nacional de Pro­ced­imien­tos Civiles y Famil­iares) will replace the Fed­eral Code of Civil Pro­ce­dure (Código Fed­eral de Pro­ced­imien­tos Civiles) as the sup­ple­men­tary law in com­mer­cial pro­ceed­ings (Arti­cles 1054 and 1063 of the Com­mer­cial Code), pur­suant to the dec­la­ra­tions of appli­ca­bil­ity and no later than April 1, 2027. The reli­a­bil­ity stan­dard is retained in the new code.

What to do and by when

  1. Clas­sify your con­tracts by risk and define which type of sig­na­ture each cat­e­gory uses: simple for low-value trans­ac­tions, advanced for sig­nif­i­cant con­tracts.
  2. Include in each con­tract a clause acknowl­edg­ing elec­tronic sig­na­tures under Arti­cles 89, 93, and 97 of the Com­mer­cial Code, and des­ig­nate each party’s infor­ma­tion system for receiv­ing mes­sages.
  3. Keep the sig­na­ture evi­dence together with the doc­u­ment: cer­tifi­cate, event log, email addresses, and dates.
  4. For sig­nif­i­cant con­tracts, obtain a reten­tion cer­tifi­cate under NOM-151-SCFI-2016.
  5. Keep the evi­dence acces­si­ble for at least ten years, even if you change plat­forms.
  6. Iden­tify the acts that require an instru­ment exe­cuted before a notary or other public offi­cer (fedatario), because those follow the rules in the third para­graph of Arti­cle 93.
  7. Set pay­ment dates in each con­tract, so as not to depend on a later formal demand.

Recommendations to mitigate risk

Sign­ing with an inad­e­quate tool does not trig­ger a fine, but it does create an evi­den­tiary risk. If the coun­ter­party denies the sig­na­ture or claims alter­ation, the com­pany must prove the reli­a­bil­ity of the method, and a PDF with no log or cer­tifi­cate offers little to do so. In a col­lec­tion action, that can mean losing the case or having to prove the rela­tion­ship with indi­rect evi­dence. In addi­tion, des­ig­nat­ing an infor­ma­tion system for receiv­ing mes­sages changes the moment at which they are deemed received (Arti­cle 91), and a ter­mi­na­tion notice sent to the wrong inbox may be deemed not received.

The elec­tronic medium does not change the rule for obli­ga­tions to give (obli­ga­ciones de dar) with­out a pay­ment date either: the cred­i­tor may only demand pay­ment thirty days after a formal demand (inter­pelación), made in court or, out of court, before a notary or two wit­nesses, under Arti­cle 2080 of the Fed­eral Civil Code (Código Civil Fed­eral). An email with a read receipt does not replace that for­mal­ity when enforce­abil­ity depends on it, which is why it is advis­able to set pay­ment dates in the con­tract instead of leav­ing the due date to a later formal demand.

Self-assessment

Answer yes or no about your own com­pany.

  1. Do you know which type of elec­tronic sig­na­ture you use for each cat­e­gory of con­tract?
  2. Do your con­tracts include a clause acknowl­edg­ing elec­tronic sig­na­tures?
  3. Do your con­tracts des­ig­nate an email address or infor­ma­tion system for receiv­ing notices?
  4. Do you keep the sig­na­ture log together with each signed doc­u­ment?
  5. Do you have a NOM-151 reten­tion cer­tifi­cate for your sig­nif­i­cant con­tracts?
  6. Could you retrieve a con­tract signed eight years ago with its com­plete sig­na­ture evi­dence?
  7. Do your con­tracts set fixed pay­ment dates, with­out depend­ing on a formal demand?

How we approach it at LEXURE

We design your com­pany’s con­tract sign­ing and reten­tion policy: which sig­na­ture to use in each case, which clauses to include, what evi­dence to keep, and how to retain it so that it with­stands an objec­tion in court. We work with inter­na­tional providers spe­cial­iz­ing in trusted elec­tronic ser­vices and adapt their tools to the require­ments of the Com­mer­cial Code.

If your con­tracts are already signed online, sched­ule a diag­nos­tic meet­ing with us and let us review whether you could prove them tomor­row.

Schedule a diagnostic meeting See our service lines

Legal basis

  1. Commercial Code (Código de Comercio), Articles 49, 80, 89, 89 Bis, 91, 93, 97, 1054, 1063, and 1298-A. Current text (opens in a new tab)
  2. NOM-151-SCFI-2016, Requirements for the retention of data messages and digitization of documents (Requisitos que deben observarse para la conservación de mensajes de datos y digitalización de documentos), DOF March 30, 2017. Text published by the Ministry of Economy (opens in a new tab)
  3. Federal Tax Code (Código Fiscal de la Federación), Article 17-D. Current text (opens in a new tab)
  4. Federal Civil Code (Código Civil Federal), Article 2080. Current text (opens in a new tab)
  5. National Code of Civil and Family Procedure (Código Nacional de Procedimientos Civiles y Familiares), Articles 348 to 350. Current text (opens in a new tab)

This note is for information only and describes the law in force on the verification date. It is not legal advice on a specific matter. It is a translation of the Spanish original: Mexican law is published in Spanish, and the official Spanish texts prevail.

Keep reading

Related notes.

See all notes