Thank you for your reply and time.
I am sorry that I may not have stated my problem.
I want to use only PAC file through fiddlercore, and I don't want to include "RegisterAsSystemProxy" (as Calvin said at the beginning of the post).
In fact, what I want to do is to use fiddlercore to implement only a specific application, without affecting the operation of other applications, just as fiddler can do. What I know is that when I use the "Any Process(drag this icon to a window to show traffic from only that process)" function of fiddler, he can only proxy the application I want. I don't know how fiddler implements this function. Maybe he just uses oS.Ignore() like fiddlercore?
I have seen your discussion with Hendrik in this post, which has benefited me a lot. I adopted "idea 1", but I encountered a problem later, I don't want to affect other applications, I just want to proxy what I want, but if I don't include "RegisterAsSystemProxy" in FiddlerCoreStartupFlags, PAC file will not take effect. What have I missed?
This is the problem I encountered，please could you advise me.