It appears that I can not delete all existing bookmarks in a pdf with out saving after the delete then saving again after the add. Is that expected?
Below does not remove the existing bookmarks:
//Delete the existing bookmarks and replace with ours
_pdfBookmarkEditor = new Aspose.Pdf.Kit.PdfBookmarkEditor();
_pdfBookmarkEditor.BindPdf(Orig_File);
_pdfBookmarkEditor.DeleteBookmarks();
_pdfBookmarkEditor.CreateBookmarkOfPage(BookMarkName, 1);