using (MemoryStream stream = new MemoryStream(pdfAsBinary))
{
    using (PdfReader reader = new PdfReader(pdfAsBinary))
    {
        using (Document doc = new Document(PageSize.A4))
        {
            PdfWriter writer = PdfWriter.GetInstance(doc, stream);
            PdfImportedPage page = writer.GetImportedPage(reader, 1);


            image = Image.GetInstance(page);
            using (var pdfStream = new FileStream(tempPath, FileMode.Create, FileAccess.ReadWrite, FileShare.Read))
            {
                 PdfWriter pdfwriter = PdfWriter.GetInstance(doc, pdfStream);
                 doc.Open();
                 doc.SetPageSize(PageSize.A4);
                 image.ScalePercent(30f);
                 doc.Add(image);
                 doc.Close();
             }
         }
    }
 File.Copy(tempPath, pathToFile);
 }

private static byte[] resizeToA4(byte[] inputDoc)
{
    using (MemoryStream out = new MemoryStream())
    {
        using (PdfReader reader = new PdfReader(inputDoc))
        {
            using (Document doc = new Document(PageSize.A4))
            {
                PdfWriter writer = PdfWriter.GetInstance(doc, out);
            }
        }
    return outPDF.ToArray();
    }