How to touch a file in C#?

System.IO.File.SetLastWriteTimeUtc(fileName, DateTime.UtcNow);

If you don’t know whether the file exists, you can use this:

if(!System.IO.File.Exists(fileName)) 
    System.IO.File.Create(fileName).Close();   // close immediately 

System.IO.File.SetLastWriteTimeUtc(fileName, DateTime.UtcNow)