Refresh document in notepad++

@Milan Pandey solution is perfect.

Just in case some one don't want to auto update all files but only single file then easiest solution would be,

Note - In case if icon not available then View -> Monitoring(tail -f)

I frequently use it to monitor changes in log files.

EDIT on 2020-04-10: as per Eric Hirst's comment here below (thanks!) apparently now this feature is mapped out of the box to Ctrl + R.

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Yes, the Reload from Disk feature is built-in. By default it's not mapped to any keyboard shortcut, though, so you will have to do it yourself:

Settings -> Shortcut mapper

then choose Modify and map it to your favorite hotkey. Mine is usually mapped to Ctrl + R.

Notepad++ has a file monitoring option that is designed for log files. The following extract from the release notes describes the facility and how to use it.

Notepad++ 6.9.2 released

18 May 2016 01:23:00

Log Monitoring is one of most wanted features. It is in v6.9.2 now. As indicated its name, Log Monitoring allows users to monitor log files' writting, update by scrolling to the last line while every modification, just like Unix command "tail -f". Click on "eye icon" on toolbar or use menu "View->Monitoring (tail -f)" to activate/disactivate this command