string fileToSendToDevice = @"C:\Text.txt";
OpenNETCF.Desktop.Communication.RAPI rApi = new OpenNETCF.Desktop.Communication.RAPI();
if (!rApi.DevicePresent) return; // no active sync
if (!rApi.Connected) rApi.Connect();
if (!File.Exists(fileToSendToDevice)) return; // file not found
rApi.CopyFileToDevice(fileToSendToDevice,
Path.Combine(@"\My Documents\", Path.GetFileName(fileToSendToDevice)));