@Drache22, if you're using the Smart Home version of the TRIGGERcmd Alexa skill, your commands are like Smart Home switches that you're turning on or off.
If you enable parameters, make your voice word PC, and put your shutdown command in the "Off Command" field, then you can say, "Alexa, desligar PC."
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If you use the non-Smart Home skill, you could keep your voice field as "desligar pc" and say: "Alexa, pergunte Execute Comando executar desligar pc."