I am trying to migrating to a new PC and I realized that I have unsaved notes in Notepad++. Apparently, they are a lot and saving it one by one is a tedious tasks. So upon searching, this is the best recommendation:

1. Ensure to check the settings from: Settings > Preferences > Backup > Remember current session for next launch
2. Check this folder  %USER%\AppData\Roaming\Notepad++\backup
3. Copy the files, no need to convert. You can open it using any text editor.