Could be treated as new feature or bug.
Use case or problem
So problem is that Obsidian built in PDF-viewer does not seem to allow the use of special characters in file name. Problem occurred using nordic characthers Ö, Ä, Å , but seems to apply to other special characters too (Extended ASCII?).
Problem occurs if file name and/or file path at any point has these characters used.
Problem was reproduced in sandbox mode and with another computer with fresh install.
Proposed solution
Add support for special characters in PDF file names. Maybe ASCII characters 192-255 fills typical use case requirement? Or whatever is the industry standard to handle it.
Current workaround (optional)
Open in default PDF viewer or change folder and file names not to include special characters.