How to Fix Invalid Digital Signature Token in Acrobat on macOS
Question details
The user is encountering an error in Adobe Acrobat where a hardware-based digital signature credential is fundamentally recognized as invalid on macOS.
- Product
- Adobe Acrobat
- Device & OS
- macOS
- Scenario
- Attempting to digitally sign a PDF document using a physical hardware token or smart card on a Mac.
- Observed behavior
- Acrobat displays an error message stating that the selected digital signature credential is not valid, preventing the document from being signed.
Ensure your hardware token is securely connected to a working USB port on your Mac and that you have administrator privileges to install or update the required middleware.
Verify Drivers, Certificates, and Acrobat Configuration
Use this method to ensure that all required software components (Acrobat, token driver, middleware) are fully compatible with your current macOS version and correctly configured.
Digital signature hardware tokens require dedicated middleware to communicate with macOS and Adobe Acrobat. If the middleware is outdated or incompatible with your OS version (like macOS Mojave or later), the signature will show as invalid.
Unplug the hardware token from your Mac, wait a few seconds, and plug it back securely into a direct USB port rather than a hub.
Visit your token provider's official website to confirm that your currently installed token driver and middleware officially support your specific version of macOS.
Open your token provider's middleware application or the macOS Keychain Access tool to confirm that your digital certificate is still active and has not been revoked or expired.
In Adobe Acrobat, go to the 'Preferences' menu, select 'Signatures', and under 'Identities & Trusted Certificates', click 'More'. Ensure your specific hardware token credential is selected as the default signing method.
Contact the Certificate Authority (CA)
Proceed with this solution if your certificate shows as valid but fails consistently, or if the credential works for only a brief period (e.g., one day).
Sign PDF Documents Securely with WPS Office
If you are unable to resolve complex hardware token and middleware errors in Adobe Acrobat, you can easily handle, edit, and sign your PDF documents using WPS Office. It provides a robust, built-in PDF toolset for Mac users.
- 1. Launch WPS Office: Open WPS Office on your Mac and load the PDF document you need to sign.
- 2. Access the Signature Tool: Navigate to the 'Fill & Sign' or 'Insert' tab on the top ribbon and click on 'Sign'.
- 3. Create Your Signature: Select the option to create a new signature. You can type your name, draw your signature using your trackpad, or insert an image of your signature.
- 4. Apply and Save: Drag the newly created signature to the designated signature line in your document, resize if necessary, and save your PDF.
Frequently Asked Questions
Why does Adobe Acrobat say my digital signature is invalid on Mac?
This commonly occurs if the hardware token's middleware is not fully compatible with your current macOS version, the token is improperly connected, or the certificate itself has expired.
How do I check if my digital certificate has expired on macOS?
You can check the expiration date by opening the Keychain Access application on your Mac, or by opening the dedicated token management software provided by your Certificate Authority.
Will my hardware token work with PDF readers other than Acrobat?
Yes, as long as the alternative PDF software supports macOS Keychain integration or allows you to load the specific PKCS#11 module provided by your token manufacturer.
