The %xxx% notation is how Windows handles environment variables. %AppData% is one of the standard system environment variables (since at least Windows XP), which expands to the path where Windows likes storing per-application user-data.

Environment variables can be used in virtually any standard Windows interface – whether it’s the cmd.exe or PowerShell command-line shells or a batch script; or whether it’s in the Windows Explorer (file/folder browser), where you can type it into the address bar; or whether it’s a File Open or File SaveAs window; or whether it’s a registry entry for associating a file with Notepad++ (or some other program).

On standard Windows configurations for Windows Vista, 7, 8, 10, and 11, %AppData% expands to C:\Users\<user name>\AppData\Roaming.

On older systems (Win 2000, Win XP), the %AppData% variable refers to C:\Documents and Settings\<user name>\Application Data by default.

On neither older systems nor newer systems do you need to include Roaming after the %AppData%, because the %AppData% variable already includes Roaming in the value.

Thus trying to make use of %AppData%\Roaming\Notepad++ will expand to C:\Users\<user name>\AppData\Roaming\Roaming\Notepad++. This is not likely where you will find the configuration files.

When many people write %AppData%\Roaming\Notepad++, they are really attempting to indicate that it’s ...\AppData\Roaming\Notepad++ – they see the \Roaming after the word AppData in the expanded path, so they assume that they can shortcut that to %AppData%\Roaming\Notepad++. However, that will likely not work:

External References:

• Microsoft Help Page

  %APPDATA%
        Windows XP and Windows 2000	C:\Documents and Settings\<user name>\Application Data
        Windows 10, Windows 8.1, Windows 7, and Windows Vista	C:\Users\<user name>\AppData\Roaming
  

• SS64’s Environment Variables page

  %APPDATA% => C:\Users\{username}\AppData\Roaming
  

• http://environmentvariables.org/AppData

• Wikipedia article

  %AppData%
        * XP => C:\Documents and Settings\{username}\Application Data
        * Vista / 7 / 8 => C:\Users\{username}\AppData\Roaming