Should I write to invite a professor to be my PhD thesis examiner? My supervisor has already invited formally the professor to be my examiner.
Do I need to invite the professor personally as he may learn more about my work? 
Is there any conflict of interest to do so?
The way in which doctoral examiners are selected will differ between countries, between universities within countries, and within schools. Ask your supervisor for advice on what you should do here and follow their instructions.