How to add "Open with Notepad++" (Portable) to Windows Context Menu?

Instructions on how to do this here: https://npp-user-manual.org/docs/shell-extension/

In short, download the dll, register and voila!

I've had a much simpler way I've used for ages. Save this as a file called Notepad++.right-click.reg:

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\*\shell\Edit with Notepad++]
"Icon"=hex(2):43,00,3a,00,5c,00,50,00,72,00,6f,00,67,00,72,00,61,00,6d,00,20,\
  00,46,00,69,00,6c,00,65,00,73,00,20,00,28,00,78,00,38,00,36,00,29,00,5c,00,\
  4e,00,6f,00,74,00,65,00,70,00,61,00,64,00,2b,00,2b,00,5c,00,6e,00,6f,00,74,\
  00,65,00,70,00,61,00,64,00,2b,00,2b,00,2e,00,65,00,78,00,65,00,00,00

[HKEY_CLASSES_ROOT\*\shell\Edit with Notepad++\command]
@="C:\\Program Files (x86)\\Notepad++\\notepad++.exe %1"

Then just double-click it and choose Yes!

Edit
Amend the second entry to point to the Notepad++ executable as pointed out by @Sun, especially important if you install the 64 bit version.

This is explained in How to Add Any Application to the Windows Desktop Right-Click Menu article which says:

The first thing you’ll want to do is open up regedit.exe through the Start Menu search or run box, and then browse down to the following key: HKEY_CLASSES_ROOT\Directory\Background\shell

The screen should look similar to this one if you are in the right place.

Next, you’ll want to create a new key underneath the shell key, the name of which is exactly what is going to show up on the desktop menu. Right-click on the “shell” key, and then choose New \ Key from the menu.

Give the new key the name that you want to show up on the desktop context menu. For this example we’ll be using Open with Notepad++.

Next you’ll need to create the command key that will actually hold the command used to launch the application. Right-click on the new Notepad++ key, and then choose New \ Key from the menu.

Give this key the name “command” in lowercase.

To complete this step you’ll need the full path to the application that you want to launch. You can use Shift + Right-Click to get the Copy as Path menu item to find this more quickly.

Now click on “command” on the left side, and then double-click on the (Default) key in the right side to edit the string value.

Paste in the full path to the executable that you got from the “Copy as Path” step above, or you can put in the full path yourself if you’d like.

And right-clicking on the desktop will produce the new menu item… naturally, using this menu item should launch Notepad++.

You can add as many applications to the desktop context menu as you’d like, just repeat the steps again with a new menu item name.

It is basically the same for other Windows versions too.

If the registry tweaking suggestion from Saimak is not something you want to try, adding a shortcut to the EXE file to the "Send To" list will allow you to right click any item and get it open in Notepad++.

The easiest way to access the "Send To" folder within which to create the shortcut is to enter shell:sendto in the Run box and press enter.