What are the applicable processor for the ATmega32u4? And what are higher versions of ATmega32u4?
The Arduino Uno cannot use the Keyboard library. The microcontroller needs to have a native USB interface. The Uno uses the Atmega328p, which does not have one.

You can use the Arduino Micro or Arduino Leonardo for this.



For more experienced hackers: If you need to use the Uno, but still want to use extended USB capabilities (more than USB to Serial), it is possible to reprogram the Atmega32U4 on the Uno, which is only used as USB to Serial adapter chip, but of course has native USB capabilities and could create a HID/Keyboard input on the USB interface. Since that is not a task for beginners, it is not applicable for this question, but should be mentioned for future readers.