How to write File Synchronization Function with C#

Question

Hello! I would like to know how to write File Synchronization function, use which Windows API? Does it File System API? How I can Hook File System API write File? The requirement of my File Synchronization function is listed on below: 1) Two different location servers e.g. Hong Kong and USA 2) When Hong Kong's server updated a file named as Record.xls, the newly wrote data will be written into USA server's Record.xls. 3) The method is not use copy and paste, just write the updated data into the other location's server Record.xls file. If anyone know how to write the File Synchronization function, please give me reply asap. Thanks!