Public Shared Sub CreateEncryptedDocument(pdfFilename As String, images As Vintasoft.Imaging.ImageCollection, password As String)
    ' create encryption system 40-bit RC4, password protection
    Dim encryption As New Vintasoft.Imaging.Pdf.Security.EncryptionSystem(Vintasoft.Imaging.Pdf.Security.EncryptionAlgorithm.RC4, 40, password, password, Vintasoft.Imaging.Pdf.Security.UserAccessPermissions.AllowAll)

    ' create encrypted document
    Using document As New Vintasoft.Imaging.Pdf.PdfDocument(Vintasoft.Imaging.Pdf.PdfFormat.Pdf_14, encryption)
        ' add pages
        For Each image As Vintasoft.Imaging.VintasoftImage In images
            document.Pages.Add(image)
        Next

        ' save document
        document.SaveChanges(pdfFilename)
    End Using
End Sub

public static void CreateEncryptedDocument(
    string pdfFilename, 
    Vintasoft.Imaging.ImageCollection images, 
    string password)
{
    // create encryption system 40-bit RC4, password protection
    Vintasoft.Imaging.Pdf.Security.EncryptionSystem encryption = 
        new Vintasoft.Imaging.Pdf.Security.EncryptionSystem(
            Vintasoft.Imaging.Pdf.Security.EncryptionAlgorithm.RC4, 40,
            password, password, 
            Vintasoft.Imaging.Pdf.Security.UserAccessPermissions.AllowAll);

    // create encrypted document
    using (Vintasoft.Imaging.Pdf.PdfDocument document = new Vintasoft.Imaging.Pdf.PdfDocument(
        Vintasoft.Imaging.Pdf.PdfFormat.Pdf_14, encryption))
    {
        // add pages
        foreach (Vintasoft.Imaging.VintasoftImage image in images)
            document.Pages.Add(image);

        // save document
        document.SaveChanges(pdfFilename);
    }
}