//// 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.AcroForms;using GrapeCity.Documents.Text;using System.Security.Cryptography.X509Certificates;
namespace DsPdfWeb.Demos{    // This sample generates and signs a PDF (using code that is similar to SignDoc sample),    // and then signs the generated PDF with a second signature without invalidating the original    // signature, by using incremental update (default when using the Sign() method).    public class SignIncremental    {        public int CreatePDF(Stream stream)        {            var doc = new GcPdfDocument();            // Load a signed document (we use code similar to the SignDoc sample):            doc.Load(CreateAndSignPdf());            // Init a second certificate:            var pfxPath = Path.Combine("Resources", "Misc", "JohnDoe.pfx");            var cert = new X509Certificate2(File.ReadAllBytes(pfxPath), "secret",                X509KeyStorageFlags.MachineKeySet | X509KeyStorageFlags.PersistKeySet | X509KeyStorageFlags.Exportable);            var sp2 = new SignatureProperties()            {                SignatureBuilder = new Pkcs7SignatureBuilder()                {                    CertificateChain = new X509Certificate2[] { cert }                },                Location = "DsPdfWeb Demo Browser",                SignerName = "DsPdfWeb",                SigningDateTime = Common.Util.TimeNow(),            };            // Find the 2nd (not yet filled) signature field:            var sfld2 = doc.AcroForm.Fields["SecondSignature"] as SignatureField;            // Connect the signature field and signature props:            sp2.SignatureField = sfld2 ?? throw new Exception("Unexpected: could not find 'SecondSignature' field");            // Sign and save the document:            doc.Sign(sp2, stream);
            // Rewind the stream to read the document just created             // into another GcPdfDocument and verify all signatures:            stream.Seek(0, SeekOrigin.Begin);            var doc2 = new GcPdfDocument();            doc2.Load(stream);            foreach (var fld in doc2.AcroForm.Fields)                if (fld is SignatureField sfld)                    if (!sfld.Value.VerifySignatureValue())                        throw new Exception($"Failed to verify signature for field {sfld.Name}");
            // Done (the generated and signed document has already been saved to 'stream').            return doc.Pages.Count;        }
        // This method is almost exactly the same as the SignDoc sample,        // but adds a second signature field (does not sign it though):        private Stream CreateAndSignPdf()        {            var doc = new GcPdfDocument();            var page = doc.NewPage();            var tf = new TextFormat() { Font = StandardFonts.Times, FontSize = 14 };            page.Graphics.DrawString("Hello, World!\n" +                "Signed TWICE by DsPdfWeb SignIncremental sample.",                tf, new PointF(72, 72));
            // Init a test certificate:            var pfxPath = Path.Combine("Resources", "Misc", "DsPdfTest.pfx");            var cert = new X509Certificate2(File.ReadAllBytes(pfxPath), "qq",                X509KeyStorageFlags.MachineKeySet | X509KeyStorageFlags.PersistKeySet | X509KeyStorageFlags.Exportable);            var sp = new SignatureProperties()            {                SignatureBuilder = new Pkcs7SignatureBuilder()                {                    CertificateChain = new X509Certificate2[] { cert }                },                Location = "DsPdfWeb Demo Browser",                SignerName = "DsPdfWeb",                SigningDateTime = Common.Util.TimeNow(),            };
            // Init a signature field to hold the signature:            var sf = new SignatureField();            sf.Widget.Rect = new RectangleF(72, 72 * 2, 72 * 4, 36);            sf.Widget.Page = page;            sf.Widget.BackColor = Color.LightSeaGreen;            // Add the signature field to the document:            doc.AcroForm.Fields.Add(sf);            // Connect the signature field and signature props:            sp.SignatureField = sf;
            // Add a second signature field:            var sf2 = new SignatureField() { Name = "SecondSignature" };            sf2.Widget.Rect = new RectangleF(72, 72 * 3, 72 * 4, 36);            sf2.Widget.Page = page;            sf2.Widget.BackColor = Color.LightYellow;            // Add the signature field to the document:            doc.AcroForm.Fields.Add(sf2);
            var ms = new MemoryStream();            doc.Sign(sp, ms);            return ms;        }    }}