Question: I would like to know if it is possible to find out when a file is added to a folder in C#. I know you can see the time of creation and many other things in the FileInfo, but nok when it was added.

Answer: 
Check out the FileSystemWatcher class - <http://msdn.microsoft.com/en-us/library/system.io.filesystemwatcher.aspx>

You'll find a complete example towards the bottom of the page.
For "snapshot" solution is possible to use this library <https://github.com/igorcrevar/Directory-Snapshot-Difference-Csharp>