iTextSharp problem concatenating PDF documents

I am trying to build up a single PDF from a bunch of other PDFs that I am filling out some form values in. Essentially I am doing a PDF mail merge. My code is below:

byte[] completedDocument = null;
using (MemoryStream streamCompleted = new MemoryStream())
{
    using (Documen开发者_开发技巧t document = new Document())
    {
    document.Open();
    PdfCopy copy = new PdfCopy(document, streamCompleted);
    copy.Open();

    foreach (var item in eventItems)
    {
        byte[] mergedDocument = null;
        PdfReader reader = new PdfReader(pdfTemplates[item.DataTokens[NotifyTokenType.OrganisationID]]);
        using (MemoryStream streamTemplate = new MemoryStream())
        {
            using (PdfStamper stamper = new PdfStamper(reader, streamTemplate))
            {
                foreach (var token in item.DataTokens)
                {
                    if (stamper.AcroFields.Fields.Any(fld => fld.Key == token.Key.ToString()))
                    {
                        stamper.AcroFields.SetField(token.Key.ToString(), token.Value);
                    }
                }
                stamper.FormFlattening = true;
                stamper.Writer.CloseStream = false;
            }

            mergedDocument = new byte[streamTemplate.Length];
            streamTemplate.Position = 0;
            streamTemplate.Read(mergedDocument, 0, (int)streamTemplate.Length);
        }
        reader = new PdfReader(mergedDocument);

        for (int i = 1; i <= reader.NumberOfPages; i++)
        {
            document.SetPageSize(PageSize.A4);
            copy.AddPage(copy.GetImportedPage(reader, i));
        }
    }
}
completedDocument = new byte[streamCompleted.Length];
streamCompleted.Position = 0;
streamCompleted.Read(completedDocument, 0, (int)streamCompleted.Length);

}

The problem I am having is that is throws a null reference exception when it exits the using (Document document = new Document()) block.

From debugging the iTextSharp source the problem is the below method in PdfAnnotationsimp

public bool HasUnusedAnnotations() {
            return annotations.Count > 0;
        }

annotations is null so this throws the null ref exception. Is there something I should be doing to instantiate this?

I changed:

document.Open();
PdfCopy copy = new PdfCopy(document, streamCompleted);

to

PdfCopy copy = new PdfCopy(document, streamCompleted);
document.Open();

And it fixed the problem. This library needs better exception handling. When you do something slightly wrong it falls over horribly and gives you no clue about what you did wrong. I have no idea how i could possibly have worked this out if I didn't have the source code.

What version of iTextSharp are you using? The Document class doesn't implement IDisposable so you can't wrap it in a using block.