When browsing archive from krusader and opening a pdf from archive Okular complains with the following error: Could not open krarc:*****.pdf. Reason: Could not start process Unable to create io-slave: klauncher said: Unknown protocol 'krarc' Could this protocol be implemented in ocular
This seems to me like a bug in krusader to me. I'd suggest you open a bug for them, they should not be expecting other apps to understand their custom url schemes.