''' <summary>
''' Changes action of the first bookmark of PDF document.
''' </summary>
''' <param name="pdfFilename">The filename of PDF document.</param>
Public Shared Sub ChangeFirstBookmarkAction(pdfFilename As String)
    ' open PDF document
    Using document As New Vintasoft.Imaging.Pdf.PdfDocument(pdfFilename)
        ' create goto action to the last page of PDF document
        Dim dest As New Vintasoft.Imaging.Pdf.Tree.PdfDestinationFit(document, document.Pages(document.Pages.Count - 1))
        Dim newAction As New Vintasoft.Imaging.Pdf.Tree.PdfGotoAction(dest)

        ' get the first bookmark of PDF document
        Dim bookmark As Vintasoft.Imaging.Pdf.Tree.PdfBookmark = document.Bookmarks(0)
        ' change the action of bookmark
        bookmark.Action = newAction

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

/// <summary>
/// Changes action of the first bookmark of PDF document.
/// </summary>
/// <param name="pdfFilename">The filename of PDF document.</param>
public static void ChangeFirstBookmarkAction(string pdfFilename)
{
    // open PDF document
    using (Vintasoft.Imaging.Pdf.PdfDocument document = 
        new Vintasoft.Imaging.Pdf.PdfDocument(pdfFilename))
    {
        // create goto action to the last page of PDF document
        Vintasoft.Imaging.Pdf.Tree.PdfDestinationFit dest = 
            new Vintasoft.Imaging.Pdf.Tree.PdfDestinationFit(document, document.Pages[document.Pages.Count - 1]);
        Vintasoft.Imaging.Pdf.Tree.PdfGotoAction newAction = 
            new Vintasoft.Imaging.Pdf.Tree.PdfGotoAction(dest);
        
        // get the first bookmark of PDF document
        Vintasoft.Imaging.Pdf.Tree.PdfBookmark bookmark = document.Bookmarks[0];
        // change the action of bookmark
        bookmark.Action = newAction;

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