File was updated, how to know?

Hi,
I have the situation where my VC++ MDI application is presenting the contents of multiple files
in different windows. If any of the files is updated by an external app my application window must be made aware of this, so that it can keep the contents of it's window concurrent.
How do I do this? I need Windows to send my app a message so it can reload the contents of the file.
Any suggestions and I will be grateful.
Best regards
Gustav

Read about FindFirstChangeNotification Function

... or ReadDirectoryChangesW

Super! Thank you for your advice, will start to implement right away.
/Gustav