Open file with existing instance of Notepad++ portable

The program that you're pointing to isn't registered correctly.

In regedit: Navigate to Computer\HKEY_CLASSES_ROOT\Applications and find your .exe name. Navigate under its name to shell>open>command. In the Default change its location to the actual location of the executable, hit okay and then try and reassociate the file type as you normally would.

Source: http://answers.microsoft.com/en-us/windows/forum/windows_7-files/problems-with-file-association-in-windows-7-64-bit/8a84fcec-22df-4942-8e35-d98dbe96e327

Here is the hack that may work for you.

Requirements:

1. Two Portable Notepad++ in two separate folders. (It may work with one NPP installation, but two separate Notepad++ seem to be cleaner approach. You may also not need Portable Notepad++, but it may be easier that way.)
2. Two or more virtual desktops

How does it work: (I have animated GIF at the end to demonstrate this steps).

1. Open Notepad++ folder on the first Virtual Desktop.
2. Right click on Notepad++.exe to create a shortcut.
3. Right click on the newly created shortcut and go to its properties.
4. Add -multiInst in the target section. (The text is case-sensitive, and there is a space at the beginning.)
5. Click OK to close the properties.
6. Double click on the shortcut.
7. It should open the new instance of Notepad++ in that virtual desktop.
8. Now switch to another Virtual Desktop. Open its own Notepad++ folder. And follow steps 2-7.
9. To keep things organized, I kept two folders, VM1 and VM2 with the notepad++ folders in them. (VM being Virtual Machine)

Some Final Notes:

• This would work as long as the Notepad++ window in a virtual machine was Active, i.e. you had touched it at least once.
• This is because when you open text file (or your source code files), it opens in the Last Active instance of Notepad++.
• I am assuming that you are not changing your virtual desktops very frequently, since that would nullify the actual purpose of virtual desktops.

Here is the animated GIF.

• You can right click on GIF and open it in new tab to see the steps clearly.

• GIF shows steps on one virtual desktop, you need to replicate it on the other too.

  

I hope it is helpful. Thanks.