To send audio from the audio file to the SoundModem, you have to install Virual Audio Cable.
Now play the audio file to de Virtual Sound Cable Device.
Start Audio player like VLC .
And open SoundModem->Settings->Devices and select AFSK AX.25 1200 bd and decoding process will start.
Thanks to all the students and Ham Radio that produce this knowledge in GranaSAT team.