Problem with PDF Bookmarks

I used the sample code that was given to extract PDF bookmarks. It did not work. I got an error “Object reference not set to an instance of an object.”

'create PdfBookmarkEditor
Dim bookmarkEditor As New PdfBookmarkEditor

'open PDF file
bookmarkEditor.BindPdf(Server.MapPath("DevelopersGuide.pdf"))

'extract bookmarks
Dim thebookmarks As Bookmarks
thebookmarks = bookmarkEditor.ExtractBookmarks()
NumberOfBookmarks = thebookmarks.Count

For Each bookmark As Bookmark In thebookmarks
    Console.WriteLine("Title: {0}", bookmark.Title)
    Console.WriteLine("Page Number: {0}", bookmark.PageNumber)
Next bookmark

Hi Joseph,

Thanks for using our products.

Can you please share the source PDF document so that we can test the scenario at our end. We apologize for your inconvenience.