How to get ckeditors value from wpf webbrowser

So im working on my final school project for software engineer. And my project was some kind of cms that lets people to add their own post to my application. I have this unknown way which is really slowing down my work. The unknown way is: -I want to get the instance value of ckeditor inside my webbrowser.

I have tried to load php file to webbrowser but its no good.

here is my source code in the add post form:

public add_post()
    {
        InitializeComponent();
        W1.Navigate("C:\\Users\\AkihiroKisaragi\\source\\repos\\Application_Tutor\\Application_Tutor\\newpost.php");
        MainWindow w = new MainWindow();
        w.buttonmenu.Visibility = Visibility.Collapsed;
    }

and this is the basic code to the html:

Summary:

i just want to know the way to get the value of ckeditor in the webbrowser from the c# codes..

thankyou in advance