Notepad++ comes with autocomplete enabled by default.
You can disable it if you want. Here’s how to do it (in this case, I’m using a Windows 10 PC):
Hit Settings at the top.
Click on Preferences.
In the Preferences pop-up, select Auto-Completion.
Uncheck Enable auto-completion on each input.
You can enable the autocomplete at any time by selecting the above mentioned Enable auto-completion on each input.
Also, keep in mind:
From these three options, you can select the one you want autocomplete for:
Function completion (only for functions), Word completion (only for words), and Function and word completion (for both functions and words).
You can also specify the number of characters (1 to 9) after which the autocomplete list will appear.
Ignore numbers – if selected, Auto-Completion ignores the number.
Function parameters hint on input – if this option is selected it means you will see the parameters of a function as a hint while using it.