SUMMARY If the pdf file is in a hidden folder, like ~/.cache/evolution/tmp/... okular is unable to open the file. STEPS TO REPRODUCE 1. Put a pdf in a folder ~/.test 2. Try to open OBSERVED RESULT Could not open file://~/.teste/pdf EXPECTED RESULT Open the pdf SOFTWARE/OS VERSIONS Snap package ADDITIONAL INFORMATION
Nothing we can do about this unfortunately. It's a defect in snapd which simply doesn't let the snap access .cache. This may get solved with a revised file access system though. If you feel particularly brave you could try taking this to forum.snapcraft.io, I would assume .cache/evoluation/tmp/* could be whitelisted somewhere, of course the general problem of not being able to open host-side caches remains for other applications.