How to Add a CAC Signature to a PDF

CAC (Common Access Card) signatures are used for official government or military documents.

We’ll walk you through the CAC signing process, explain what you need, and show you how to fix common errors along the way.

How to CAC Sign a PDF – Step-by-Step Guide

If you already have your CAC set up and your computer is configured, signing a PDF only takes a few minutes. Here's how to CAC sign a PDF using standard tools.

Step 1: Connect Your CAC Reader

• Plug in your CAC reader
• Insert your CAC card
• Wait for your system to detect the card (this may take a few seconds)

Make sure the middleware software for your card (like ActivClient) is installed and up to date.

Step 2: Open the PDF in a Compatible Viewer

• Use our PDF Reader
• Open the file you want to sign
• If you want to lock it for security reasons, use Protect PDF.

Step 3: Add the CAC Signature

• Click the Sign option or select Digital Signatures in your viewer
• Choose your CAC certificate from the list
• Follow the prompt to enter your PIN
• Place the signature on the page and save the file

This process lets you digitally sign PDF with CAC and ensures authenticity and compliance with security standards.

Requirements for Using Your CAC to Sign PDF

Before you can add CAC signature to PDF files, you need:

• A working CAC reader with USB connection
• Your CAC card, inserted correctly
• Middleware software like ActivClient or built-in support for smart cards
• A PDF viewer that supports digital certificates
• Access to your PIN when prompted Sign PDF works for basic signature workflows, but CAC cards require a local certificate interface.

How to Fix Common CAC Signature Problems

Running into issues while signing? Here’s how to fix common CAC problems:

• Nothing happens when you insert the card → Restart your computer and check that your middleware software is running
• The signature option is grayed out → The PDF might be protected—try unlocking it or flattening it first
• The certificate isn’t showing up → Reinstall your CAC drivers or try a different PDF viewer
• The file won’t save after signing → Save the file under a new name or export a copy instead

Still not working? Try signing a different file to test your setup. If that works, the issue may be with the original PDF.

FAQs

1. Why can’t you digitally sign PDF with CAC?

Your system may be missing the required certificate drivers, or the PDF app you’re using doesn’t support smart card authentication.

2. Can I sign a PDF without removing the CAC card?

Yes. The card must remain inserted while signing. Removing it will interrupt the process.

3. Is a CAC digital signature legally valid?

Yes. CAC-based signatures are legally recognized for federal use and meet identity verification and data integrity standards.

4. How do I add a CAC signature to a secure PDF?

First, unlock the file if needed using Unlock PDF. Then reopen the file in your CAC-compatible reader and sign.

5. Can I add multiple CAC signatures to one PDF?

Yes. As long as each signer has their own CAC and access to the file, multiple digital signatures can be added in sequence.

6. Can someone else use my CAC card to sign documents?

No. Your CAC is tied to your identity and requires your PIN. Never share your card—it’s like handing over your ID and password.

7. Can you sign PDFs with a CAC card without internet?

Yes. Signing happens locally on your machine. As long as your drivers and certificates are set up, internet access is not required.