Private Shared Sub AcquireImagesAndSaveToStreamAsPdf()
        ' create the device manager
        Using deviceManager As New Vintasoft.Twain.DeviceManager()
                ' open the device manager
                deviceManager.Open()

                ' select the device in the default device selectio ndialog
                deviceManager.ShowDefaultDeviceSelectionDialog()

                ' get reference to the selected device
                Dim device As Vintasoft.Twain.Device = deviceManager.DefaultDevice

                ' specify that device UI must not be used
                device.ShowUI = False
                ' specify that device must be closed after scan
                device.DisableAfterAcquire = True

                ' acquire images from device
                Dim acquireModalState As Vintasoft.Twain.AcquireModalState = Vintasoft.Twain.AcquireModalState.None
                Dim mem As System.IO.MemoryStream = Nothing
                Dim firstImage As Boolean = True
                Do
                        acquireModalState = device.AcquireModal()
                        Select Case acquireModalState
                                Case Vintasoft.Twain.AcquireModalState.ImageAcquired
                                        ' save all acquired images as PDF stored in the memory
                                        If firstImage Then
                                                ' get the first image as PDF stored in the memory
                                                mem = device.AcquiredImage.GetAsStream(New Vintasoft.Twain.ImageEncoders.TwainPdfEncoderSettings())
                                                firstImage = False
                                        Else
                                                ' add image to PDF stored in the memory
                                                device.AcquiredImage.Save(mem, New Vintasoft.Twain.ImageEncoders.TwainPdfEncoderSettings())
                                        End If

                                        ' dispose the acquired image
                                        device.AcquiredImage.Dispose()
                                        Exit Select
                        End Select
                Loop While acquireModalState <> Vintasoft.Twain.AcquireModalState.None

                ' Upload stream data to the server or doing something else...
                ' ...

                ' close the device
                device.Close()

                ' close the device manager
                deviceManager.Close()
        End Using
End Sub

static void AcquireImagesAndSaveToStreamAsPdf()
{
    // create the device manager
    using (Vintasoft.Twain.DeviceManager deviceManager = new Vintasoft.Twain.DeviceManager())
    {
        // open the device manager
        deviceManager.Open();

        // select the device in the default device selectio ndialog
        deviceManager.ShowDefaultDeviceSelectionDialog();

        // get reference to the selected device
        Vintasoft.Twain.Device device = deviceManager.DefaultDevice;

        // specify that device UI must not be used
        device.ShowUI = false;
        // specify that device must be closed after scan
        device.DisableAfterAcquire = true;

        // acquire images from device
        Vintasoft.Twain.AcquireModalState acquireModalState = Vintasoft.Twain.AcquireModalState.None;
        System.IO.MemoryStream mem = null;
        bool firstImage = true;
        do
        {
            acquireModalState = device.AcquireModal();
            switch (acquireModalState)
            {
                case Vintasoft.Twain.AcquireModalState.ImageAcquired:
                    // save all acquired images as PDF stored in the memory
                    if (firstImage)
                    {
                        // get the first image as PDF stored in the memory
                        mem = device.AcquiredImage.GetAsStream(new Vintasoft.Twain.ImageEncoders.TwainPdfEncoderSettings());
                        firstImage = false;
                    }
                    else
                    {
                        // add image to PDF stored in the memory
                        device.AcquiredImage.Save(mem, new Vintasoft.Twain.ImageEncoders.TwainPdfEncoderSettings());
                    }

                    // dispose the acquired image
                    device.AcquiredImage.Dispose();
                    break;
            }
        }
        while (acquireModalState != Vintasoft.Twain.AcquireModalState.None);

        // Upload stream data to the server or doing something else...
        // ...

        // close the device
        device.Close();

        // close the device manager
        deviceManager.Close();
    }
}