@HITESHREE LOKHANDE ,
As we are mainly responsible for general issues of Office desktop applications, if you want to know more information about the develpment of Office clients, it's best to post questions on the forums below. Thanks for your understanding.
Office developer community
Microsoft Office for Developers
Besides, here is a link wihch I think it maybe helpful to your question. "In which programming language is Microsoft Office written?"
(Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)
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