'''' This code is part of Document Solutions for PDF .NET demos.'' Copyright (c) MESCIUS inc. All rights reserved.''Imports System.IOImports System.DrawingImports GrapeCity.Documents.PdfImports GrapeCity.Documents.Pdf.AcroFormsImports GrapeCity.Documents.TextImports System.Security.Cryptography.X509Certificates
'' 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    Function CreatePDF(ByVal stream As Stream) As Integer        Dim doc = New GcPdfDocument()
        '' Load a signed document (we use code similar to the SignDoc sample):        doc.Load(CreateAndSignPdf())
        '' Init a second certificate:        Dim pfxPath = Path.Combine("Resources", "Misc", "JohnDoe.pfx")        Dim cert = New X509Certificate2(File.ReadAllBytes(pfxPath), "secret",                X509KeyStorageFlags.MachineKeySet Or X509KeyStorageFlags.PersistKeySet Or X509KeyStorageFlags.Exportable)        Dim sp2 = New SignatureProperties() With {            .SignatureBuilder = New Pkcs7SignatureBuilder() With {.CertificateChain = New X509Certificate2() {cert}},            .Location = "DsPdfWeb Demo Browser",            .SignerName = "Jaime Smith",            .SigningDateTime = Util.TimeNow()        }
        '' Find the 2nd (not yet filled) signature field:        Dim sfld2 = CType(doc.AcroForm.Fields("SecondSignature"), SignatureField)        '' Connect the signature field and signature props:        If sfld2 Is Nothing Then            Throw New Exception("Unexpected: could not find 'SecondSignature' field")        End If        sp2.SignatureField = sfld2
        '' 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)        Dim doc2 = New GcPdfDocument()        doc2.Load(stream)        For Each fld In doc2.AcroForm.Fields            If TypeOf fld Is SignatureField Then                Dim sfld = CType(fld, SignatureField)                If Not sfld.Value.VerifySignatureValue() Then                    Throw New Exception($"Failed to verify signature for field {sfld.Name}")                End If            End If        Next        ''        '' Done (the generated and signed document has already been saved to 'stream').        Return doc.Pages.Count    End Function
    '' This method is almost exactly the same as the SignDoc sample,    '' but adds a second signature field (does not sign it though):    Private Function CreateAndSignPdf() As Stream        Dim doc = New GcPdfDocument()        Dim page = doc.NewPage()        Dim tf = New TextFormat() With {.Font = StandardFonts.Times, .FontSize = 14}        page.Graphics.DrawString("Hello, World!" + vbLf +            "Signed TWICE by DsPdfWeb SignIncremental sample.",            tf, New PointF(72, 72))
        '' Init a test certificate:        Dim pfxPath = Path.Combine("Resources", "Misc", "DsPdfTest.pfx")        Dim cert = New X509Certificate2(File.ReadAllBytes(pfxPath), "qq",            X509KeyStorageFlags.MachineKeySet Or X509KeyStorageFlags.PersistKeySet Or X509KeyStorageFlags.Exportable)        Dim sp = New SignatureProperties() With {            .SignatureBuilder = New Pkcs7SignatureBuilder() With {                .CertificateChain = New X509Certificate2() {cert}            },            .Location = "DsPdfWeb Demo Browser",            .SignerName = "DsPdfWeb",            .SigningDateTime = Util.TimeNow()        }
        '' Init a signature field to hold the signature:        Dim 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:        Dim sf2 = New SignatureField() With {.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)
        Dim ms = New MemoryStream()        doc.Sign(sp, ms)        Return ms    End FunctionEnd Class