You can use perfectly to emphasize an adjective or adverb, especially when you think the person you are talking to might doubt what you are saying.
There's no reason why you can't have a perfectly normal child.
没有理由说明你生不出一个完全正常的孩子。
You know perfectly well what happened.
你完全清楚发生了什么。
If something is done perfectly, it is done so well that it could not possibly be done better.
This ambitious adaptation perfectly captures the spirit of Kurt Vonnegut's acclaimed novel.
这次大胆的改编完美地把握住了库尔特·冯内古特那部广为称赞的小说的精髓。