receive wbDO_DocumentCompleted event within task.RunSynchronously

Galera,

I'm implementing a code to download pdf's from a particular site.

Debugging it, I discovered that the tasks were asynchronous and the counter was lost and it ended up getting some page without downloading.

I changed the process to a task around the clock (task.RunSynchronously).

Following code:

while (numeroPagina <= qtdePaginas){

            var task = new Task<long>(() => {

                paginaCarregada = false;

                urlPesquisa = urlPesquisaOriginal;
                urlPesquisa = urlPesquisa.Replace("datatrocar", dataFiltro);

                urlPesquisa = urlPesquisa.Replace("first", numeroPagina.ToString());
                wbDO.Navigate(urlPesquisa);    

                return numeroPagina++;
            });

            task.RunSynchronously();
                                       }

However, I have not received the wbDO_DocumentCompleted event that downloads the sample itself:

private void wbDO_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {    
            string pagina;

            pagina = wbDO.Document.Body.Parent.OuterHtml;

            if (download)
            {    
                DownloadDocumentos(wbDO.Document.Body.Parent.OuterHtml);
            }
            else
                PesquisarData();
        }

Could you help me understand what happened?