Hi Christian.
While an Android can connect directly to a Bluetooth device using App Inventor, App Inventor 2 apps cannot connect directly to a PC or Mac computer. You need an interface to do that (for example your Arduino).
Are you attempting to create a text editor within your app or trying to control and edit text on a computer from an Android?
You might be able to use Using LINUX commands in App Inventor. Extension depending on what you actually want to do.