First of all, please read my comment to the question...
If there's no process which locks file during read/write operation, there's no chance to find out if specific file is "completed" or no. But...
There's a
FileSystemWatcher Class (System.IO)[
^], which is listening for file system change notifications and raises events when a directory, or file in a directory, changes. See the list of:
FileSystemWatcher Events (System.IO)[
^]
Good luck!