C# - open multiple pages in WebBrowser and send a command to all of them

I have a winform app with the following functionality:

1. Has a multiline textbox that contain one URL on each line - about 30 URLs (each URL is different but the webpage is the same (just the domain is different);


2. I have another textbox in which I can write a command and a button that sends that command to an input field from the webpage.

The webpage consist of a textbox and a button which I want to be clicked after I insert a command in that textbox.

My code so far:

//get path for the text file to import the URLs to my textbox to see them
private void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog fbd1 = new OpenFileDialog();
            fbd1.Title = "Open Dictionary(only .txt)";
            fbd1.Filter = "TXT files|*.txt";
            fbd1.InitialDirectory = @"M:\";
            if (fbd1.ShowDialog(this) == DialogResult.OK)
                path = fbd1.FileName;

        }


//import the content of .txt to my textbox
        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Lines = File.ReadAllLines(path);
        }

//click the button from webpage
private void button3_Click(object sender, EventArgs e)
        {
    this.webBrowser1.Document.GetElementById("_act").InvokeMember("click");
        }


//parse the value of the textbox and press the button from the webpage
        private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            newValue = textBox2.Text;
            HtmlDocument doc = this.webBrowser1.Document;
            doc.GetElementById("_cmd").SetAttribute("Value", newValue);

        }

Now, how can I add all those 30 URLs from my textbox in the same webcontroller so that I can send the same command to all of the textboxes from all the webpages and then press the button for all of them ?