Notepad++ provides 2 types of features for auto-completion and suggestions:
To enable it, you need to change a setting.
Settings
> Preferences...
> Auto-completion
Enable Auto-completion on each input
Function parameter hint on input
to display parameters while typing a function name (c.f. picture below)To use it, start to type a word or a function and after the number of characters you have specified, the suggestions will appear:
Some documentation about auto-completion is available here: http://docs.notepad-plus-plus.org/index.php/Auto_Completion