I am a PhD student and have a D in one of my exams due to some family issues. I also have a B in 3 subjects and A in one. I am worried about my future. will the D have an impact on my job prospects even if I maintain my GPA above 3.3?
It depends on where you live. In the US, most tech companies weight GPA low (but still relevant). There's only a soft correlation between GPA and performance. That being said, it doesn't give you an excuse to slack off.
Furthermore, for PhDs most people assume that you have bad grades as you're focusing on research.
With both these facts, I hope you will not worry about it.