Make a Digital Tin on Arduino write text symbols on computer

Morning,

Is it possible to use the usb connection of the Mega 2560 Rev3 to transform a digital input into a specific text key in the computer?

Not easily (you either need to flash special firmware onto the 16u2, which would interfere with normal functionality, or use software on the computer to connect to it over serial, and make a virtual keypress in response)

With a Micro/Leo/Due/Zero it is super easy to send keypress events using the Keyboard library; these devices have native USB on the microcontroller you're programming, so they can appear as a hardware keyboard to the computer.

Okay so I will use the Arduino Due instead, thanks for replying!