public void UnirListaPdf(List<String> InFiles, String OutFile)
    {
        var o = 0;
        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;
            InFiles.ForEach(file =>
            {
                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();
                File.Delete(file);
            });
        }