Not able to delete particular bookmark,but able to update title for the same object with the following code
Document pdfDocument = new Document(“D://1.pdf”);
OutlineItemCollection CurrentItem = pdfDocument.Outlines [1];
CurrentItem.Delete();
CurrentItem.Title = “Test”;
pdfDocument.Save(path);
We managed to replicate the problem of not being able to delete the bookmark as per the given scenario. It has been logged under the ticket ID PDFNET-44145 in our bug tracking system. We have linked your post to this ticket and will keep you informed regarding any available updates.
You can remove a bookmark by name. Please refer to this help topic: Delete a Particular Bookmark from a PDF Document