By default the Notepad++ installer comes with an Shell extension. This is not really part of the Notepad++ program but very useful. If you choose to install it, then any file you rightclick on will show an entry named “Edit with Notepad++” with the Notepad++ icon.
Please note that to install or remove the extension, it sometimes is required to restart the Explorer process. For this you can reboot, logout and log back in or use the taskmanager to kill explorer (Windows NT and up) and restart it again. Hitting Ctrl+Alt+Shift+Del works too.
If the Shell extension is already installed, the Notepad++ installer cannot update or overwrite it, you first have to uninstall it and restart Explorer.