What Is a PAC in Mexico and How to Choose One

What Is a PAC and Why Do You Need One to Invoice in Mexico?

A PAC (Proveedor Autorizado de Certificación, or Authorized Certification Provider) is a company authorized by Mexico's tax authority, the SAT, to validate, stamp, and certify the CFDI (electronic invoices) that businesses issue in Mexico. When you invoice, the XML file your system generates isn't a valid invoice until a PAC reviews it, assigns it a fiscal folio, and adds the SAT's digital seal — without that step, the document has no fiscal validity with any authority.

In other words, the PAC is the mandatory middle step between your business and the SAT on every electronic invoice. It doesn't matter whether you issue invoices from an ERP, a point-of-sale system, or the SAT's free portal: somewhere in that chain, a PAC is always certifying the document.

What Is CFDI Stamping and What Role Does the PAC Play?

Stamping (timbrado) is the process that turns a CFDI from a plain XML file your software generated into a legally valid electronic invoice recognized by the SAT. Stamping isn't the same thing as "creating an invoice": almost any system can generate the XML, but stamping it — giving it legal validity — can only be done by an authorized PAC.

During stamping, the PAC does three concrete things:

• Validates that the XML meets the technical structure defined by the SAT (Anexo 20 of the Resolución Miscelánea Fiscal).
• Assigns the fiscal folio (UUID) that uniquely identifies that invoice nationwide.
• Adds the SAT's digital seal, certifying that the receipt was validated by the tax authority.

Without these three elements, the file is still just an XML — not a valid CFDI.

How the Stamping Process Works, Step by Step

Every invoice follows the same path, from the moment you generate it to the moment it comes back certified:

1. Your invoicing system generates the CFDI in XML format with the transaction details (issuer, recipient, line items, taxes).
2. The XML is signed with your Certificado de Sello Digital (CSD), a digital seal certificate that identifies your business as the issuer.
3. Your system sends that XML to the PAC you work with, usually through an API connection.
4. The PAC validates the structure, the current catalogs, and the applicable business rules.
5. If everything checks out, the PAC stamps the CFDI: it adds the fiscal folio and the SAT's digital seal.
6. The PAC reports a copy of the receipt to the SAT, as part of its regulatory obligation.
7. The stamped CFDI comes back to your system, ready to hand to the customer.

This whole process usually takes seconds when the connection between your system and the PAC is working well, which lets you invoice at the moment of sale without making the customer wait.

What a PAC Checks Before Stamping an Invoice

Not every XML gets stamped without review. The PAC applies the exact validation rules the SAT defines in Anexo 20, including:

• Whether the catalogs used (payment methods, tax regimes, product or service keys) are current.
• Whether the issuer's and recipient's tax ID (RFC) have a valid format.
• Whether the amounts, subtotals, and taxes add up correctly.
• Whether the receipt matches the current CFDI version.

If something doesn't check out, the PAC rejects the stamping request and returns the specific error, so your system or accounting team can fix it before trying again. That validation step is exactly what keeps a flawed invoice from reaching your customer or getting misregistered with the SAT — a topic we also cover in our guide on invoicing requirements in Mexico.

PAC, CSD, and Invoicing Software: Three Different Pieces

It's common to confuse the PAC with other parts of the electronic invoicing ecosystem, but each one plays a distinct role:

• The CSD (Certificado de Sello Digital) is yours, issued by the SAT, and it's what you use as the issuer to sign your receipts before sending them to be stamped. If you've never applied for one, our guide on what a CSD is explains how to get it.
• Your invoicing software is the tool that generates the XML: it could be an ERP, a point-of-sale system, or a dedicated invoicing platform.
• The PAC is the one that certifies that XML with the SAT and turns it into a valid CFDI.

Many invoicing platforms integrate the connection to one or more PACs transparently, so as an end user you sometimes don't even notice this intermediate step. But technically, no PAC means no stamping, and no stamping means no fiscally valid invoice. That's the key distinction from a related but different topic: if you want the full picture of electronic invoicing in Mexico, that guide covers the entire process; here we focus specifically on the PAC's role within it.

How to Choose a Reliable PAC for Your Business

Before contracting a PAC, it's worth checking a few concrete things:

• Confirm it's currently listed as authorized by the SAT. The SAT publishes and updates its list of authorized providers; a PAC can lose its authorization, so it's worth checking periodically, not just when you first sign up.
• Check the stability of its service. If your business stamps invoices at the moment of sale, a PAC outage means you can't invoice; ask about their track record for uptime before deciding.
• Compare pricing models. Some PACs charge per package of stamps, others by monthly subscription; the right model depends on your actual invoicing volume.
• Evaluate their technical support. When a stamping request fails mid-sale, you need to fix it fast, not wait days for a ticket response.
• Verify their API or integration is compatible with your current system, so you don't have to switch invoicing software just to switch PACs.

Several providers with years of track record and current SAT authorization operate in the Mexican market, including SW, Finkok, Sifei, Edicom, and Diverza, each with different pricing and support models. The right choice depends less on the name and more on how well it fits your invoicing volume and your existing system integration.

Common Mistakes When Working with a PAC

A few problems keep showing up in businesses that don't pay close enough attention to this part of their operation:

• Contracting a PAC without verifying it's still authorized by the SAT at the moment of purchase, not just when the original contract was signed.
• Not monitoring the PAC's status on an ongoing basis, which can leave you invoicing through a provider whose authorization has already been revoked.
• Relying on a single PAC with no backup plan, so that a service outage stops the business's invoicing entirely.
• Not validating CFDI before handing them to the customer, assuming that if the PAC stamped it, there can't be any underlying errors (like an incorrect product key).

Frequently Asked Questions

What is a PAC in simple terms?

It's the company authorized by the SAT to review, stamp, and report the digital tax receipts (CFDI) that businesses issue in Mexico. Without its validation, a CFDI has no fiscal validity.

Do I need to contract a PAC if I already use invoicing software?

It depends on the software. Many platforms already include the connection to one or more PACs as part of their service, while others only generate the XML and require you to contract stamping separately. It's worth confirming before you set up your system.

Can I switch PACs without losing my previous invoices?

Yes. Invoices that are already stamped stay on record with the SAT and in your own history, regardless of which PAC generated them. Switching providers only affects the stamping of new invoices going forward.

What happens if my PAC loses its SAT authorization?

It immediately stops being able to stamp valid receipts. That's why it's important to monitor your provider's status and avoid relying on a single PAC with no alternative, especially if your business invoices every day.

Does the PAC charge the SAT or the taxpayer?

The taxpayer. The SAT doesn't charge for stamping; the cost of the service is set by each PAC based on its own commercial model, which can vary by stamp package or subscription.

If your business is already invoicing at volume and you're tired of dealing with dropped connections, stamping errors, or mid-operation PAC switches, at AISDC we integrate CFDI invoicing directly into your systems, with automatic stamping and validations that keep errors from ever reaching your customer.