Yes, it is possible to run an external exe from a when-button-pressed trigger. We do this by the call of the procedure win_api_shell.winexec which is part of the library d2kwutil (we start the program acrobat reader). The Command-Parameter can include input-parameters for the external exe.
I don’t know if it is possible to handle the output of an external exe because we do not need this feature.
I hope this helps.