Still too ambiguous for me.
The last question and answer.

In the pdf, it says "serial cable", not "null-model cable".
So is it null-modem cable or regular serial cable?
If it is really null-modem cable, then this pdf has to be fixed.

Just answer:
null-modem
or
regular serial

Another question. In the pdf it says "Click Connect Button", and then look for the message "Serial port open success. Please turn on your box"
Is it really possible to have a "serial port open success" while the box is turned off completely?
Unless the success is only with the port at the PC's end.
And if standby mode is needed, then it might not be possible to put the box into it, if there is an emergency when the box appears to be dead.