Цикл построчного считывания файла и записи в textbox

    Private Sub Button3_Click(sender As System.Object, e As System.EventArgs) Handles Button3.Click
        Dim path As String = OpenFileDialog1.FileName
        Dim sr As StreamReader = New StreamReader(path)
        Dim i As Integer, st As String
            While sr.Peek <> -1
                i = i + 1
                st = sr.ReadToEnd
                If i = 1 Then
                    TextBox2.Text = st
                End If
                WebBrowser1.Navigate("site\" + TextBox2.Text)
            End While

TextBox1.Text = IO.File.ReadAllText(FileName)
For Each sLine In TextBox1.Lines
    MsgBox(sLine) 'Тут твои команды обработки строки
Next

Public Class Form1
 
    Private Wait As Boolean
 
    Private Sub WebBrowser1_DocumentCompleted(sender As System.Object, e As System.Windows.Forms.WebBrowserDocumentCompletedEventArgs) Handles WebBrowser1.DocumentCompleted
        Wait = False
    End Sub
 
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        TextBox1.Text = IO.File.ReadAllText(FileName)
        For Each sLine In TextBox1.Lines
            WebBrowser1.Navigate(sLine)
            Wait = True
            Do While Wait
                Application.DoEvents()
            Loop
        Next
    End Sub
 
End Class