When I use Dolphin to navigate to my home SMB share that has a bunch of PDFs (the scanner sends them all there) and open one of them, it opens them in Libreoffice Draw. I don't like that for my system default, as I prefer Okular (which also came preinstalled, so I wonder why it isn't the default). I changed the system default for PDFs to Okular and get this error message in the picture. I'm guessing it's an OS problem because of that "Input-/Output" part in the error message. However, all the other apps capable of displaying PDFs open it just fine direct from the SMB folder. Translation: "The file "smb://ben@192.168.178.4/scannershare/ScannedDoc01.pdf" could not be opened. Reason: It is not possible to establish the input/output module. Unknown protocol: "smb"."