The sample demonstrates how to decrypt an encrypted PDF document and extract the embedded picture.

using System;
using System.Drawing;
using Spire.Pdf;

namespace Decryption
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a pdf document.
            String encryptedPdf = @"Encrypted.pdf";
            PdfDocument doc = new PdfDocument(encryptedPdf, "test");

            //extract image
            Image image = doc.Pages[0].ImagesInfo[0].Image;

            doc.Close();

            //Save image file.
            image.Save("Wikipedia_Science.png", System.Drawing.Imaging.ImageFormat.Png);

            //Launching the image file.
            System.Diagnostics.Process.Start("Wikipedia_Science.png");
        }
    }
}

Imports System.Drawing
Imports Spire.Pdf

Namespace Decryption
    Friend Class Program
        Shared Sub Main(ByVal args() As String)
            'Create a pdf document.
            Dim encryptedPdf As String = "Encrypted.pdf"
            Dim doc As New PdfDocument(encryptedPdf, "test")

            'extract image
            Dim image As Image = doc.Pages(0).ImagesInfo(0).Image

            doc.Close()

            'Save image file.
            image.Save("Wikipedia_Science.png", System.Drawing.Imaging.ImageFormat.Png)

            'Launching the image file.
            Process.Start("Wikipedia_Science.png")
        End Sub
    End Class
End Namespace