What Is a CFDI?
A CFDI (Comprobante Fiscal Digital por Internet) — literally an "Internet Digital Tax Receipt" — is the official electronic invoicing document recognized by Mexico's tax authority, the Servicio de Administración Tributaria (SAT). It replaced earlier paper-based receipts and older digital formats, and for several years it has been the only accepted mechanism for documenting income, deductions, payroll, and the movement of goods for tax purposes in Mexico.
At its core, a CFDI is an XML file whose structure, fields, and allowed values are defined by the SAT. It contains the issuer's and recipient's tax details, the items or services billed, applicable taxes, and — crucially — a digital seal (sello digital) that guarantees the document's authenticity and integrity. This XML is typically accompanied by a PDF representation for human readability, but the legally binding document is always the sealed XML.
The Role of the SAT and PACs
The SAT sets the technical specifications, the controlled catalogs (units of measure, product/service codes, tax regimes, etc.), and the validation rules. However, the SAT does not stamp every invoice individually. Instead, it authorizes third-party companies called Proveedores Autorizados de Certificación (PACs) — Authorized Certification Providers — to do so.
The stamping (timbrado) process works as follows:
- The issuer builds the XML with all required fields and signs it using their Digital Seal Certificate (CSD).
- The signed XML is sent to the chosen PAC via its API or web portal.
- The PAC validates the structure and content, then appends the Timbre Fiscal Digital (TFD) — an additional XML node containing the PAC's own seal and the UUID folio assigned by the SAT.
- The stamped XML is returned to the issuer and delivered to the recipient.
Without a valid PAC stamp, the document has no legal tax standing.
The Digital Seal Certificate (CSD)
The CSD (Certificado de Sello Digital) is the cryptographic credential — a pair of .cer and .key files protected by a password — that allows a taxpayer to sign their CFDIs. Each RFC (tax ID) can have one or more active CSDs simultaneously. The CSD is distinct from the e.firma (formerly FIEL), which is the personal electronic signature used for general SAT proceedings; the CSD is specifically for issuing invoices. Keeping track of CSD expiry dates, renewals, and secure storage is a critical operational responsibility for any business that invoices electronically.
Types of CFDI
The SAT defines several CFDI types based on their purpose:
- Ingreso (Income): The most common type; documents a sale of goods or provision of services.
- Egreso (Expense/Credit Note): Cancels or discounts a prior income CFDI; used for returns or adjustments.
- Pago (Payment): Issued when payment is received after the invoice was already issued on credit. The Complemento de Pago (Payment Complement) records each installment, preventing VAT from being recognized twice.
- Nómina (Payroll): Documents salary and benefit payments to employees; includes a dedicated complement with IMSS and INFONAVIT fields.
- Traslado (Transfer): Certifies the lawful movement of goods; for federal road transport it must include the Carta Porte complement.
Additional sector-specific complements exist for foreign trade, in-kind payments, hydrocarbons, and others.
CFDI 4.0: The Key Changes
Version 4.0 of the CFDI standard became mandatory in early 2023, introducing notable changes over the previous version 3.3:
- Stricter recipient data: The recipient's registered name and tax regime must match SAT records exactly; a mismatch causes the PAC to reject the stamp.
- New "Exportación" field: Explicitly flags transactions related to foreign trade directly on the main invoice.
- New cancellation rules: Canceling a CFDI now generally requires the recipient's acceptance, with specific cancellation-reason codes that must be provided.
- Tax object declaration: Each line item must now explicitly state whether it is subject to tax or not, removing prior ambiguity.
These changes made accurate customer and supplier master data essential and highlighted the need for well-structured, automated invoicing pipelines.
Who Must Issue CFDIs?
Broadly speaking, any individual (persona física) or legal entity (persona moral) conducting economic activities in Mexico — sales, services, rental income, payroll — is required to issue the corresponding CFDI. The SAT defines a small number of narrow exceptions, but for the vast majority of businesses, electronic invoicing is simply mandatory.
How Businesses Automate CFDI Issuance
Manually creating invoices through the SAT's free portal or a PAC's web interface works for very low volumes, but as transaction counts grow — in e-commerce, distribution, manufacturing, SaaS billing, or recurring services — automation becomes essential.
The most common approaches are:
- Direct PAC API integration: The business connects its ERP, e-commerce platform, or custom software directly to a PAC's REST API, so CFDIs are generated and stamped in seconds without manual intervention.
- Middleware / connector layer: An intermediary service translates internal data formats to the required XML schema and handles PAC communication, error retries, and archiving.
- ERP-native modules: Platforms like SAP, Oracle, and several Mexican-market ERPs offer certified connectors to specific PACs, though customization often requires additional development.
The right architecture depends on transaction volume, existing systems, the need for custom business logic, and internal audit requirements.
If your business needs a robust, automated CFDI 4.0 integration tailored to your workflows, AISDC builds custom connectors to PACs such as factura.com, handles CSD management, and implements business-specific logic for any industry. Learn more at our CFDI invoicing services.