I have been using Kleopatra on Win10 successfully for years with MobaXTerm for SSH login using a private key stored on my Yubikey that shows up in Kleopatra’s Smartcards window.
I also have used Kleopatra with Foxit PDF until today. After a Windows update it stopped working. Instead of the prompt for my PIN from Kleopatra, I get a windows dialog that says my Yubikey isn’t suitable for this operation.
So, I was very pleased to learn that Okular was now supported. I installed Gpg4win 4.2.0. Okular GPG Edition loads OK, but does not see the key on my yubikey. There are no certificates listed in its configure backends dialog. Is this expected?
Mmh, If you have S/MIME certificates on the Yubikey and it worked before yes then this should be possible. What I find weird though is that it suddenly stopped working and you get a windows dialog though. I really hope your yubikey is fine.
My suggestion in support would be to try the following: Navigate to %APPDATA%\gnupg (that is usually c:\users\yourname\AppData\Roaming\gnupg
And there create or edit a file called scdaemon.conf and put “pcsc-shared” into that file. Then go to Kleopatra and under tools “Restart background processes” And then also restart Kleopatra. And then look into the smartcard view again.
What this is supposed to archive is that if some other application (apparently windows) that our background proccess for smartcard access accepts that and “shares” the yubikey with that. We usually try to gain exclusive access to the USB device and that might fail.
Best Regards and let us know if you have any success signing PDFs with Yubikey and Okular and also how you think Okular compares to Foxit!