[System.Runtime.InteropServices.DllImport("User32.dll")]
        static extern IntPtr SendMessage(
            IntPtr hWnd, int msg, int wParam, int[] lParam);
 
        private void Form1_Load(object sender, EventArgs e)
        {
            const int EM_SETTABSTOPS = 0x00CB;
 
            SendMessage(textBox1.Handle, EM_SETTABSTOPS, 1, new int[] { 2 });
            textBox1.Multiline = true;
            textBox1.AcceptsTab = true;
        }

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