''' <summary>
''' Instance of an external font programs controller
''' that is used for every opened PDF document.
''' </summary>
Private _fontProgramsController As Vintasoft.Imaging.Fonts.FontProgramsControllerBase

' MainForm constructor
Public Sub New()
    '....

    ' subscribe to the DocumentOpened event for managing external fonts
    AddHandler Vintasoft.Imaging.Pdf.PdfDocumentController.DocumentOpened, New System.EventHandler(Of Vintasoft.Imaging.Pdf.PdfDocumentEventArgs)(AddressOf PdfDocumentController_DocumentOpened)
    ' subscribe to the AuthenticateRequest for performing authentication

        '....
    AddHandler Vintasoft.Imaging.Pdf.PdfDocumentController.AuthenticateRequest, New System.EventHandler(Of Vintasoft.Imaging.Pdf.PdfDocumentEventArgs)(AddressOf PdfDocumentController_AuthenticateRequest)
End Sub

''' <summary>
''' Opens the PDF document.
''' </summary>
''' <param name="stream">The stream that contains PDF document.</param>
Public Sub OpenPdfDocument(stream As System.IO.Stream)
    imageViewer1.Images.Add(stream, True)
End Sub

''' <summary>
''' Handles the AuthenticateRequest event of the PdfDocumentController object.
''' </summary>
Private Sub PdfDocumentController_AuthenticateRequest(sender As Object, e As Vintasoft.Imaging.Pdf.PdfDocumentEventArgs)
    ' document is encrypted with password, authenticate as user

    Dim password As String = "userpassword"
    If e.Document.AuthenticateAsUser(password) = Vintasoft.Imaging.Pdf.Security.AuthorizationResult.IncorrectPassword Then
        System.Windows.Forms.MessageBox.Show("Incorrect user password")
    End If
End Sub

''' <summary>
''' Handles the DocumentOpened event of the PdfDocumentController control.
''' </summary>
Private Sub PdfDocumentController_DocumentOpened(sender As Object, e As Vintasoft.Imaging.Pdf.PdfDocumentEventArgs)
    ' if the instance is not created yet
    If _fontProgramsController Is Nothing Then
        ' create font programs controller common for all PDF documents
        _fontProgramsController = New Vintasoft.Imaging.Fonts.FileFontProgramsControllerWithFallbackFont(True, "fonts")
    End If
    ' use common font programs controller to manage external fonts
    e.Document.FontProgramsController = _fontProgramsController
End Sub

/// <summary>
/// Instance of an external font programs controller
/// that is used for every opened PDF document.
/// </summary>
Vintasoft.Imaging.Fonts.FontProgramsControllerBase _fontProgramsController;

// MainForm constructor
public MainForm()
{
    //....
    
    // subscribe to the DocumentOpened event for managing external fonts
    Vintasoft.Imaging.Pdf.PdfDocumentController.DocumentOpened += 
        new System.EventHandler<Vintasoft.Imaging.Pdf.PdfDocumentEventArgs>(PdfDocumentController_DocumentOpened);
    // subscribe to the AuthenticateRequest for performing authentication
    Vintasoft.Imaging.Pdf.PdfDocumentController.AuthenticateRequest += 
        new System.EventHandler<Vintasoft.Imaging.Pdf.PdfDocumentEventArgs>(PdfDocumentController_AuthenticateRequest);
    
    //....
}

/// <summary>
/// Opens the PDF document.
/// </summary>
/// <param name="stream">The stream that contains PDF document.</param>
public void OpenPdfDocument(System.IO.Stream stream)
{
    imageViewer1.Images.Add(stream, true);
}

/// <summary>
/// Handles the AuthenticateRequest event of the PdfDocumentController object.
/// </summary>
private void PdfDocumentController_AuthenticateRequest(object sender, Vintasoft.Imaging.Pdf.PdfDocumentEventArgs e)
{
    // document is encrypted with password, authenticate as user

    string password = "userpassword";
    if (e.Document.AuthenticateAsUser(password) == Vintasoft.Imaging.Pdf.Security.AuthorizationResult.IncorrectPassword)
        System.Windows.Forms.MessageBox.Show("Incorrect user password");
}

/// <summary>
/// Handles the DocumentOpened event of the PdfDocumentController control.
/// </summary>
private void PdfDocumentController_DocumentOpened(object sender, Vintasoft.Imaging.Pdf.PdfDocumentEventArgs e)
{
    // if the instance is not created yet
    if (_fontProgramsController == null)
    {
        // create font programs controller common for all PDF documents
        _fontProgramsController = 
            new Vintasoft.Imaging.Fonts.FileFontProgramsControllerWithFallbackFont(true, "fonts");
    }
    // use common font programs controller to manage external fonts
    e.Document.FontProgramsController = _fontProgramsController;
}