index.aspx.cs

protected void btnStore_Click(object sender, EventArgs e)
{
    // save the document and store in a hidden field
    // as a Base64 encoded string
    byte[] data;
    TextControl1.SaveText(out data, 
        TXTextControl.Web.BinaryStreamType.InternalUnicodeFormat);

    hiddenDocument.Value = Convert.ToBase64String(data);

    // call the 'storeDocument()' JS function
    System.Web.UI.ScriptManager.RegisterClientScriptBlock(
      this, this.GetType(),
      "CallStoreDocument",
      "storeDocument();", true);
}