Simply copy outside the container, then:
right-click with mouse inside the container shell/terminal.
If that doesn't work, reference Microsoft documentation for Copy Paste with WSL
may be necessary to enable "Use Ctrl+Shift+C/V as Copy/Paste"
# Create a mount point within the Linux container
sudo mkdir /mnt/share
# Connect the mount point to a windows network file share
sudo mount -t drvfs '\\Server\Share' /mnt/share