//// This code is part of Document Solutions for PDF .NET demos.// Copyright (c) MESCIUS inc. All rights reserved.//using System;using System.IO;using System.Drawing;using GrapeCity.Documents.Pdf;using GrapeCity.Documents.Pdf.Security;
namespace DsPdfWeb.Demos{    // This sample demonstrates the use of Security.EncryptHandler and Security.DecryptHandler.    // Security.DecryptHandler allows you to examine the security attributes of an existing PDF.    // Security.EncryptHandler allows you to specify security attributes when saving a PDF.    // DsPdf supports Standard Security Handlers revisions 2, 3, 4, 5 and 6 as defined    // in the PDF Spec 1.7 and 2.0. In this sample, we use StandardSecurityHandlerRev4.    //    // See SecurityHandlerRev6 for a Standard Security Handler revision 6 demo.    public class SecurityHandlers    {        public int CreatePDF(Stream stream)        {            // Sample passwords:            const string ownerPassword = "I'm the owner";            const string userPassword = "I'm a user";
            // Step 1: Generate a document with some security attributes:            var doc0 = new GcPdfDocument();            var rc0 = Common.Util.AddNote(                "Demonstrating security:\n" +                "In this PDF, we specify certain encryption options,\n" +                "and set owner and user passwords.",                doc0.NewPage());
            // Create a Rev4 security handler:            var ssh4 = new StandardSecurityHandlerRev4()            {                // Set some rev4 specific props:                EncryptionAlgorithm = EncryptionAlgorithm.AES,                EncryptStrings = true,            };            // StandardSecurityHandlerRev4 is derived from StandardSecurityHandlerRev3,            // so we can do this to make sure we touch rev3-specific properties only            // (the cast is for illustration only, you do not need it to set those props of course):            if (ssh4 is StandardSecurityHandlerRev3 ssh3)            {                ssh3.EditingPermissions = EditingPermissions.AssembleDocument;                ssh3.PrintingPermissions = PrintingPermissions.LowResolution;            }            // But StandardSecurityHandlerRev3 is NOT derived from StandardSecurityHandlerRev2,            // because some properties have similar meanings but different syntax, so this:            // if (ssh3 is StandardSecurityHandlerRev2 ssh2) { ... }            // will NOT work.
            // Set some passwords:            ssh4.OwnerPassword = ownerPassword;            ssh4.UserPassword = userPassword;
            // Assign the handler we created to the document so that it is used when saving the PDF:            doc0.Security.EncryptHandler = ssh4;
            // Save the PDF in a temp file, so that we can load it:            var fn = Path.GetTempFileName();            doc0.Save(fn);
            // Step 2: Load the generated PDf and examine its security attributes:            var doc = new GcPdfDocument();            using (var fs = File.OpenRead(fn))            {                // User password is needed to load the document:                doc.Load(fs, userPassword);
                // At this point we can examine doc.Security.DecryptHandler if it exists,                // but there is NO Security.EncryptHandler:                if (doc.Security.EncryptHandler != null)                    throw new Exception("This should not happen.");
                var dh = doc.Security.DecryptHandler;                if (dh is StandardSecurityHandlerRev4 dh_ssh4)                {                    // Make sure the loaded permissions are what we specified in Step 1:                    Common.Util.AddNote(                        string.Format("Security attributes that were in the loaded PDF's DecryptHandler:\n" +                            "EditingPermissions: {0}\n" +                            "PrintingPermissions: {1}",                        dh_ssh4.EditingPermissions, dh_ssh4.PrintingPermissions),                        doc.Pages[0],                        new RectangleF(72, rc0.Bottom + 36, 72 * 6, 72 * 2));                    // This won't work, sorry:                    var noway = dh_ssh4.OwnerPassword;                    if (noway != null)                        throw new Exception("No way.");                }                else if (dh is StandardSecurityHandlerRev3 dh_ssh3)                {                    // If we didn't know that we have a Rev4 handler, we would add code here,                }                else if (dh is StandardSecurityHandlerRev2 dh_ssh2)                {                    // ... and here,                }                else                {                    // ... and done something in this case too.                }
                // Save the new PDF - but PLEASE NOTE that because we did not set                // the Security.EncryptHandler, the newly saved document has no security!                doc.Save(stream);            }            // Clean up the temp file:            File.Delete(fn);            // Done:            return doc.Pages.Count;        }    }}