Helper PdfDocument support for libary itextsharp

PdfDocument.cs

public static class PdfDocument
{
    public static void AddRange(this Document document, IEnumerable<IElement> elements)
    {
        elements.ForEach(f => document.Add(f));
    }

    public static byte[] Concat(IEnumerable<byte[]> documents)
    {
        Guard.NotNullOrZeroLength(documents, nameof(documents));
        using (var ms = new MemoryStream())
        {
            var outputDocument = new Document();
            var writer = new PdfCopy(outputDocument, ms);
            outputDocument.Open();

            foreach (var doc in documents)
            {
                var reader = new PdfReader(doc);
                for (var i = 1; i <= reader.NumberOfPages; i++)
                {
                    writer.AddPage(writer.GetImportedPage(reader, i));
                }
                writer.FreeReader(reader);
                reader.Close();
            }

            writer.Close();
            outputDocument.Close();
            var allPagesContent = ms.GetBuffer();
            ms.Flush();

            return allPagesContent;
        }
    }
}