What program type is efficient to pickup the file in folder --- need an idea

Hi,

My flow is like this,

1. Another program will place a file in a folder at any time (the time is not fixed)

2. My program will pickup this file from the folder and read a content

What is the best program type in C# (winforms with interval? windows service? etc??) to handle this file after place by another program?

Need opinion.