I don't see this solution anywhere and supposedly ... according to one person, the proper way to do it is with copyPagesTo(). This does work I tested it. Your mileage may vary between city and open road driving. Goo luck.
public static bool MergePDFs(List<string> lststrInputFiles, string OutputFile, out int iPageCount, out string strError)
{
strError = string.Empty;
PdfWriter pdfWriter = new PdfWriter(OutputFile);
PdfDocument pdfDocumentOut = new PdfDocument(pdfWriter);
PdfReader pdfReader0 = new PdfReader(lststrInputFiles[0]);
PdfDocument pdfDocument0 = new PdfDocument(pdfReader0);
int iFirstPdfPageCount0 = pdfDocument0.GetNumberOfPages();
pdfDocument0.CopyPagesTo(1, iFirstPdfPageCount0, pdfDocumentOut);
iPageCount = pdfDocumentOut.GetNumberOfPages();
for (int ii = 1; ii < lststrInputFiles.Count; ii++)
{
PdfReader pdfReader1 = new PdfReader(lststrInputFiles[ii]);
PdfDocument pdfDocument1 = new PdfDocument(pdfReader1);
int iFirstPdfPageCount1 = pdfDocument1.GetNumberOfPages();
iPageCount += iFirstPdfPageCount1;
pdfDocument1.CopyPagesTo(1, iFirstPdfPageCount1, pdfDocumentOut);
int iFirstPdfPageCount00 = pdfDocumentOut.GetNumberOfPages();
}
pdfDocumentOut.Close();
return true;
}