Keyboard.press()

// use this option for OSX:
char ctrlKey = KEY_LEFT_GUI;
// use this option for Windows and Linux:
//  char ctrlKey = KEY_LEFT_CTRL;  
 
void setup() {
  // make pin 2 an input and turn on the 
  // pullup resistor so it goes high unless
  // connected to ground:
  pinMode(2, INPUT_PULLUP);
  // initialize control over the keyboard:
  Keyboard.begin();
}
 
void loop() {
  while (digitalRead(2) == HIGH) {
    // do nothing until pin 2 goes low
    delay(500);
  }
  delay(1000);
  // new document:
  Keyboard.press(ctrlKey);
  Keyboard.press('n');
  delay(100);
  Keyboard.releaseAll();
  // wait for new window to open:
  delay(1000);
}