''' <summary>
''' Changes title of the first bookmark of PDF document.
''' </summary>
''' <param name="pdfFilename">The filename of PDF document.</param>
Public Shared Sub ChangeFirstBookmarkTitle(pdfFilename As String)
    ' open PDF document
    Using document As New Vintasoft.Imaging.Pdf.PdfDocument(pdfFilename)
        ' get the first bookmark of PDF document
        Dim bookmark As Vintasoft.Imaging.Pdf.Tree.PdfBookmark = document.Bookmarks(0)
        ' change title of bookmark
        bookmark.Title = "First bookmark"

        ' save changes to a file
        document.SaveChanges()
    End Using
End Sub

/// <summary>
/// Changes title of the first bookmark of PDF document.
/// </summary>
/// <param name="pdfFilename">The filename of PDF document.</param>
public static void ChangeFirstBookmarkTitle(string pdfFilename)
{
    // open PDF document
    using (Vintasoft.Imaging.Pdf.PdfDocument document = 
        new Vintasoft.Imaging.Pdf.PdfDocument(pdfFilename))
    {
        // get the first bookmark of PDF document
        Vintasoft.Imaging.Pdf.Tree.PdfBookmark bookmark = document.Bookmarks[0];
        // change title of bookmark
        bookmark.Title = "First bookmark";

        // save changes to a file
        document.SaveChanges();
    }
}