This is not only one questionnaire but different questionnaires measuring different things. Most of them have been tested to be valuable on what they measure. It means that you can trust them if you use them as they are.
If you think it'd be more precise, you can do some adaptations like replacing "the system" by your product's name or replacing "in my job" by "in my activity", to make the questionnaire fits your case better.
But you have to be careful because the validity of this questionnaire is tested for the precise word it uses. It means that if you change it, you might not measure anymore what you want to measure.
Example: do not replace something like "I would find it useful" by "I would find it great". It's not measuring the same thing anymore.
Hope it helps.