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

The sample demonstrates how to decrypt a document.

private void button1_Click(object sender, EventArgs e)
{
    string fileName = OpenFile();
    if (!string.IsNullOrEmpty(fileName))
    {
        //Create word document
        Document document = new Document();
        document.LoadFromFile(fileName,FileFormat.Doc,this.textBox1.Text);

        //Save doc file.
        document.SaveToFile("Sample.doc", FileFormat.Doc);

        //Launching the MS Word file.
        WordDocViewer("Sample.doc");
    }


}

private string OpenFile()
{
    openFileDialog1.Filter = "Word Document (*.doc)|*.doc";
    openFileDialog1.Title = "Choose a document to Decrypt";

    openFileDialog1.RestoreDirectory = true;
    if (openFileDialog1.ShowDialog() == DialogResult.OK)
    {
        return openFileDialog1.FileName;
    }

    return string.Empty;
}

private void WordDocViewer(string fileName)
{
    try
    {
        System.Diagnostics.Process.Start(fileName);
    }
    catch { }
}

Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles button1.Click
	Dim fileName As String = OpenFile()
	If Not String.IsNullOrEmpty(fileName) Then
		'Create word document
		Dim document_Renamed As New Document()
		document_Renamed.LoadFromFile(fileName,FileFormat.Doc,Me.textBox1.Text)

		'Save doc file.
		document_Renamed.SaveToFile("Sample.doc", FileFormat.Doc)

		'Launching the MS Word file.
		WordDocViewer("Sample.doc")
	End If


End Sub

Private Function OpenFile() As String
	openFileDialog1.Filter = "Word Document (*.doc)|*.doc"
	openFileDialog1.Title = "Choose a document to Decrypt"

	openFileDialog1.RestoreDirectory = True
	If openFileDialog1.ShowDialog() = DialogResult.OK Then
		Return openFileDialog1.FileName
	End If

	Return String.Empty
End Function

Private Sub WordDocViewer(ByVal fileName As String)
	Try
		Process.Start(fileName)
	Catch
	End Try
End Sub