keyboard and mouse interface
An Arduino based on the ATmega32u4 can do this, performing the function of both the microcontroller and keyboard/mouse emulator.

For example: Arduino Leonardo, Yun or Arduino Micro.

The Arduino Micro is nice because of its form factor.



The library support for USB keyboard and mouse emulation is readily available to make a project like yours very easy.

This code snippet opens a new document by emulating CNTRL-N

   // new document:
  Keyboard.press(ctrlKey);
  Keyboard.press('n');
  delay(100);
  Keyboard.releaseAll();
  // wait for new window to open:code