.NET secondary development

Hello everyone, I am studying .NET secondary development, but unfortunately, when I refer to the secondary development on YouTube’s official website to add references, my document does not have the dll file in the video. I tried adding the dll file I already had, but every time I added it my visual studio would crash. If anyone knows what this problem is and would like to help me, I would be grateful.
My visual component version is 4.6, and the visual studio version is 2017.