Pin windows on top, control their transparency, and jump straight to the file behind them.
Press Ctrl+Win+Alt+P to pin or unpin the current window so it stays on top of others. You can also do this from the window's system menu (right-click its title bar, or press Alt+Space).
Press Ctrl+Win+Alt+S, or choose Opacity... from the window's system menu, to open an opacity dialog for the current window. Window+ remembers your transparency and pin settings per application, so they're restored the next time you open it.
Press Ctrl+Win+Alt+E, or use the system menu's File submenu, to show the file the active window has open in File Explorer. From the same submenu you can comment on that file or copy a link to it directly to your clipboard.
Press Ctrl+Win+Alt+Shift+Left or Ctrl+Win+Alt+Shift+Right to dock the active window to that side of the screen. Press Ctrl+Win+Alt+Shift+Down to undock it. You can change these shortcuts and the docked width in Settings.
Open Settings to set pin or opacity rules for specific applications or window titles, or to exclude certain applications from Window+ entirely.