Niet)ondersteund algoritme - Unsupported algoritme

[Koen225142565mmt]

I have a new (Belgian) eID. But the certificates were not longer recognised. So I re-Installed Adobe Acrobat Reader DC. The certificate for signature is now accepted and tested (5 green check marks). But at the end of the process to sign a .pdf document the error appears: (dutch:) “Fout aangetroffen tijdens ondertekenen: Niet-ondersteund algoritme” (free translated:)”Error encountered while signing: Unsupported algorithm”. What can I do? Please answer.

[Senne22794518b6zp]

I'm having the same issue, Did you find a solution yet?

[try67]

Contact the authority that issued this signature profile and ask for exact instructions on how to use it.

It's also recommended to go to the application's Preferences (via the Edit menu on Windows or the Reader app menu on a Mac), then to Trust Manager and click both Update Now buttons there.

[Koen225142565mmt · Accepted solution]

The problem is solved. Solution : configure Acrobat Reader without pkcs#11 module.
If this module has already been linked, the already linked module must therefore be uncoupled again.
After unlinking, restart Acrobat Reader and try signing again.
BELGIUM uses software called eID middleware that communicates with the card for Windows. In the past Acrobat Reader could not use this middleware and Acrobat Reader needed the pkcs11 module to do the communication with the card. Recently, ADOBE has made the necessary changes so that READER can work with the middleware.
The pkcs11 module has now basically become optional within Acrobat Reader.

[chantala61760780]

Thanks, this helped me also, on Belgium eid-website it's mention to couple the pkcs module

[mathias_4680]

After removing the pkcs11 module there is no certificate shown to use to sign? Or am I missing something? I'm on MacOS 15.6.

[shah_2804]

I'm having the same issue. Of course after removing Pkcs11 there is no Root path with the signature. But with pkcs11 the signature can't be placed " unsupported algorithm". Spent 8 hrs on Adobe support, they couldn't help

[danielc29258241]

Romania, mac M4, same problem ....

[AnandSri]

Hello @danielc29258241

I hope you are doing well, and thanks for reaching out.

This error typically occurs when Acrobat Reader encounters a cryptographic algorithm it does not support for digital signatures. Common scenarios:

• Using PKCS#11 modules unnecessarily with eID middleware.
• Certificates or smartcards using algorithms not recognized by Acrobat (e.g., certain ECC or GOST variants).
• Outdated Acrobat version lacking support for newer algorithms.

Please ensure you have the latest version of Acrobat or Reader installed: 25.001.20693 Planned update, Sept 09, 2025. Check for any pending updates from the Menu > help > check for updates, install the updates, restart the app and the machine, and try again.

Remove PKCS#11 Module (if linked): 

Go to Menu > Preferences > Signatures > Identities & Trusted Certificates > More.
If a PKCS#11 module is linked, unlink it.
Restart Acrobat Reader and try signing in again.

Update Trust Manager Settings: In Menu > Preferences > Trust Manager, click Update Now for both options to refresh trusted root certificates.

See these articles for more information:

https://adobe.ly/4gjm4BB

https://adobe.ly/469Sfjz

https://adobe.ly/4mgUR3R

Thanks,

Anand Sri.

[danielc29258241]

10q for your reply, 

if i unlink the PKCS#11 module then with middleware running when i want to sign the popup say Digital ID Configuration Required, -> configure digital id -> use a signature creation device -> continue. ... Adobe Acrobat could not find any new digital IDs. If your digital ID is on a hardware token, please make sure it is plugged in and the token interface is properly configured. Contact your system administrator fo further assistance.

im trying so digitaly sign PDF with new romanian CEI .... 

i have the latest acrobat version

[AnandSri]

Hello @danielc29258241

I hope you are doing well, and thanks for sharing the additional details.

When the PKCS#11 module is unlinked, Acrobat no longer has a way to communicate with your smart card or token. Even if the middleware is running, Acrobat needs the module explicitly configured to access the digital ID. 

• Re-link the PKCS#11 Module:

  • Go to: Menu > Preferences > Signatures > Identities & Trusted Certificates > More...
  • Under PKCS#11 Modules and Tokens, click Attach Module.
  • Browse to the correct .dll (Windows) or .dylib (macOS) file provided by your token vendor (e.g., CEI Romania).
  • Confirm and restart Acrobat.

• Ensure Middleware is Up to Date:

  • Download the latest version of the CEI middleware from the official Romanian eID site.
  • Reinstall it and reboot your system.

See this community dscussion for more details: https://adobe.ly/4mdgWQD

Thanks,

Anand Sri.