The
default method of opening unknown files forces you to go through a
list of known applications and is generally a pain to deal with. That’s
why I like to have a context menu option for “Open with Notepad” so
that I can quickly open up files without having to go through a lot of
trouble.
This registry hack is
nothing new, it’s been around forever. Also note that you can use this
same technique to substitute any other application that you’d like by
adjusting the path in the registry to point to the different editor.

Manual Registry Hack
Open regedit.exe through the start menu search or run box, and then browse down to the following key:
HKEY_CLASSES_ROOT\*\shell

Right-click on “shell” and
choose to create a new key, calling it “Open with Notepad”. Create a
new key below that one called “command”. Double-click on the (Default)
value in the
right-hand pane and enter in the following:
notepad.exe %1
The change should take effect immediately… just right-click on any file and you’ll see the next menu entry.
Download Registry Hack
Just
download, extract and double-click on the OpenWithNotepad.reg file to
enter the information into the registry. There’s also an uninstall
script included.