Unable to load pkcs11 module for digital signing

I've experienced the same issue and after a couple of hours of research on the web, I have realized that there are two versions of the pkcs11 library on the computer: 32-bit pkcs11.dll at "C:/Windows/SysWOW64/" and 64-bit pkcs11.dll at "C:/Windows/System32/".

In my case, I was using the pkcs11 library at the 32-bit location. (I did not know this then) By 2023 Adobe has ceased support for 32-bit Acrobat, and the Acrobat on my computer silently upgraded to 64-bit by one of the routine updates. I did not even realize this update until experiencing this issue. So, my new 64-bit Acrobat stopped working with my 32-bit pkcs11.dll.

Unfortunately, Acrobat gives a generic error when you try to add the wrong-bit library to the Identities & Trusted Certificates section. So it is not easy to find what is wrong.

On the other hand, the solution is simple:

- If you have 32-bit Acrobat, use 32-bit pkcs11.dll at "C:/Windows/SysWOW64/"

- If you have 64-bit Acrobat, use 64-bit pkcs11.dll at "C:/Windows/System32/"

I hope this solution works for you.

Acrobat requires the pkcs11 library to be signed.