Thank you very much for your quick reply. The following are the sample code we use to extract pages. version is 8.0.1.40, run time version is v4.0.30319. it is 32 bit.
Our PDF is highly confidential, and can not provide them. sorry about that.
doc = new PdfDocument(Path.Combine(workFolder, fileNameWithExtension));
MergeOptions options = new MergeOptions(true);
options.Outlines = false;
MergeDocument firstPdf = new MergeDocument(doc, start, end - start + 1, options);
firstPdf.Draw(Path.Combine(splitFolder,outlines[i].Text.Split(':')[1].Trim() + ".pdf"));