CopyFile.cs

var oldPath = "C:\\Users\\Admin\\AppData\\Roaming\\Skype\\My Skype Received Files\\man.png";
 var filename = string.Format("C:\\Users\\Admin\\Desktop\\{0}",Path.GetFileName(oldPath));//.Dump();
   using(FileStream s = File.Open(oldPath, FileMode.Open)){
   MemoryStream t = new MemoryStream();
     s.CopyTo(t);
	 
	  var result = t.ToArray();
	 
	  using (FileStream SourceStream = File.Open(filename, FileMode.OpenOrCreate))
            {
                SourceStream.Seek(0, SeekOrigin.End);
                SourceStream.Write(result, 0, result.Length);
            }
   }