How to automatically reload modified files in Notepad++

You can disable the confirmation in the settings:

Settings -> Preferences -> MISC. -> Update silently

There is a nice plugin called Document monitor (Can be found and installed from the Plugins => Plugin Manager => show Plugin Manager menu),

It updates the opened files every 3 seconds. Together with the option to "scroll to last line after update", it will have the ability to "tail" a log file as wanted.

After the plugin installation don't forget to activate it by clicking:

Plugins => Document monitor => start to monitor

For monitoring an individual log file, use the View > Monitoring (tail -f) option (thanks to https://superuser.com/a/1246651/17025).

This will keep the file up to date, and also keep the end of the file visible (which is not always exactly what you want); it also is a setting for each individual file rather than a global setting.

This approach is not usable if you want to edit the file as well - it keeps it in read-only mode.