He got a forged certificate so that he could get a promotion and a better salary
Question

My brother got a forged academic certificate so that he could get promoted to a new position. When he presented the certificate he got the promotion. Is the salary that he gets regarded as haram, and what should he do?.
Praise be to Allah.What you brother did, forging the certificate in order to get a promotion at work, is a haram action, because it involves lying, forgery and taking a salary that he does not deserve. 
Whatever is based on that falsehood is also false, and it is not permissible for him to take the extra salary that was given to him after he was promoted on the basis of that false certification. 
What he must do is repent to Allah and go back to his old position, or leave that company and work to obtain a new certificate that will qualify him for the position he wants. 
See also question no. 279129 . 
And Allah knows best.