using IronPdf;

// Create a new PDF or edit an existing document.
PdfDocument Pdf = PdfDocument.FromFile("existing.pdf");

// Add bookmark
Pdf.Bookmarks.AddBookMarkAtEnd("Author's Note", 2);
Pdf.Bookmarks.AddBookMarkAtEnd("Table of Contents", 3);

// Store new bookmark in a variable to add nested bookmarks to
var summaryBookmark = Pdf.Bookmarks.AddBookMarkAtEnd("Summary", 17);

// Add a sub-bookmark within the summary
var conclusionBookmark = summaryBookmark.Children.AddBookMarkAtStart("Conclusion", 18);

// Add another bookmark to end of highest-level bookmark list
Pdf.Bookmarks.AddBookMarkAtEnd("References", 20);

Pdf.SaveAs("existing.pdf");

Imports IronPdf

' Create a new PDF or edit an existing document.
Private Pdf As PdfDocument = PdfDocument.FromFile("existing.pdf")

' Add bookmark
Pdf.Bookmarks.AddBookMarkAtEnd("Author's Note", 2)
Pdf.Bookmarks.AddBookMarkAtEnd("Table of Contents", 3)

' Store new bookmark in a variable to add nested bookmarks to
Dim summaryBookmark = Pdf.Bookmarks.AddBookMarkAtEnd("Summary", 17)

' Add a sub-bookmark within the summary
Dim conclusionBookmark = summaryBookmark.Children.AddBookMarkAtStart("Conclusion", 18)

' Add another bookmark to end of highest-level bookmark list
Pdf.Bookmarks.AddBookMarkAtEnd("References", 20)

Pdf.SaveAs("existing.pdf")