string usuario = ConfigurationManager.AppSettings["usrConsultaNAS"];
string password = ConfigurationManager.AppSettings["passConsultaNAS"];

NetworkCredential NCredentials = new NetworkCredential(usuario, password);

using (new NetworkConnection(rutaCarpetasNAS, NCredentials))
{
    using (FileStream stream = new FileStream(OutFile, FileMode.Create))
    {
        using (Document doc = new Document())
        {
            using (PdfCopy pdf = new PdfCopy(doc, stream))
            {
                doc.Open();

                PdfReader reader = null;
                PdfImportedPage page = null;

                foreach (var file in InFiles)
                {
                    reader = new PdfReader(file);
                    for (int i = 0; i < reader.NumberOfPages; i++)
                    {
                        page = pdf.GetImportedPage(reader, i + 1);
                        pdf.AddPage(page);
                    }
                    pdf.FreeReader(reader);
                    reader.Close();
                }
            }
        }
    }
}