Notepad++ File Association

File Associations within an app do not work for PortableApps packaged versions. In all cases in-app file associations will bypass the stuff that we use to make it portable.

This means that when you run the app from an associated file, you are leaving files, folders, registry entries or worse (personal data) behind and often won't be using the settings you would expect (eg launching Firefox Portable from an association would make you use a new profile with none of your saved settings, history or bookmarks).

For the most part we developers attempt to stop in-app file type associations from working where we can. I would guess that Notepad++ may be one of those apps.

If you really do need to associate files with a PortableApp you do have a few avenues to follow:
1) Manually associate files with the AppNamePortable.exe instead of through the app itself
2) Use a third party app to do it (search here for eXpresso, there is also another one I always forget the name of)
3) Wait a little longer - file associations will be part of the PortableApps Platform in an upcoming release.