How can I "open" a file from WSL with the default application?
A recent answer for WSL 2: Just do wslview slides.pdf.
This is a part of the wslu collection and was pre-installed in my Ubuntu. Unfortunately, the documentation is a bit sparse.
All the cmd.exe variants didn't work for me, because it doesn't want to open inside a path like \\wsl$\…
Since the Windows Linux interop started working you can now call:
cmd.exe /C start <file>