How instant does it need to be?
If it needs to be real time, then you will need something that can hook the file io interupts (and they can/will be busy).
If it does not need to be realtime, a simple app that runs in the background and checks a file every x mins may be good enough.
eg: a batch file run as an at/schedule job.
How many files does it need to monitor
How often does the check need to happen.
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