https://www.c-sharpcorner.com/article/visual-studio-creating-and-managing-digital-certificates-in-c-sharp/
https://www.programmersought.com/article/757711306/

var store = new X509Store(StoreLocation.CurrentUser); 

store.Open(OpenFlags.ReadOnly); 

var certificates = store.Certificates;
foreach (var certificate in certificates)
{
    var friendlyName = certificate.FriendlyName;
    var xname = certificate.GetName(); //obsolete
    Console.WriteLine(friendlyName);
}




/ STEP 1
mycerRoot = generateRootCertV1("MY_CA"); // Tried also generateRootCertV2(BouncyCastle)
addCertToStore(mycerRoot, StoreName.Root, StoreLocation.LocalMachine);

// STEP 2
mycer = generateCert("127.0.0.1", mycerRoot); // ?????? <-- Something like that How to implement generateCert??
addCertToStore(mycer, StoreName.My, StoreLocation.LocalMachine);

public static Org.BouncyCastle.X509.X509Certificate generateRootCertV2(string certName)
{
    X509V1CertificateGenerator certGen = new X509V1CertificateGenerator();

    X509Name CN = new X509Name("CN=" + certName);

    RsaKeyPairGenerator keypairgen = new RsaKeyPairGenerator();
    keypairgen.Init(new KeyGenerationParameters(new SecureRandom(new CryptoApiRandomGenerator()), 1024));

    AsymmetricCipherKeyPair keypair = keypairgen.GenerateKeyPair();

    certGen.SetSerialNumber(BigInteger.ProbablePrime(120, new Random()));
    certGen.SetIssuerDN(CN);
    certGen.SetNotAfter(DateTime.MaxValue);
    certGen.SetNotBefore(DateTime.Now.Subtract(new TimeSpan(7, 0, 0, 0)));
    certGen.SetSubjectDN(CN);
    certGen.SetPublicKey(keypair.Public);
    certGen.SetSignatureAlgorithm("MD5WithRSA");

    Org.BouncyCastle.X509.X509Certificate newCert = certGen.Generate(keypair.Private);

    return newCert;
}

public static X509Certificate2 GenerateRootCertV1(string HostNameOrIP_or_CertName)
{
    X509Certificate2 cert = null;

    try
    {
        using (CryptContext ctx = new CryptContext())
        {
            ctx.Open();
            cert = ctx.CreateSelfSignedCertificate(
                new SelfSignedCertProperties
                {
                    IsPrivateKeyExportable = true,
                    KeyBitLength = 4096,
                    Name = new X500DistinguishedName("cn=" + HostNameOrIP_or_CertName),
                    ValidFrom = DateTime.Today.AddDays(-1),
                    ValidTo = DateTime.Today.AddYears(20),
                });
        }
    }
    catch (Exception ex)
    {
    }

    return cert;
}

public static bool addCertToStore(X509Certificate2 cert, StoreName st, StoreLocation sl)
{
    bool bRet = false;

    try
    {
        X509Store store = new X509Store(st, sl);
        store.Open(OpenFlags.ReadWrite);

        if (cert != null)
        {
            byte[] pfx = cert.Export(X509ContentType.Pfx);
            cert = new X509Certificate2(pfx, (string)null, X509KeyStorageFlags.PersistKeySet | X509KeyStorageFlags.MachineKeySet);

            if (!certExists(store, cert.SubjectName.Name))
            {
                store.Add(cert);
                bRet = true;
            }
        }
        store.Close();
    }
    catch
    {

    }
    return bRet;
}
c#
.net



 PdfLoadedDocument document = new PdfLoadedDocument("D:\\How to set Variable in eBMR Software.pdf");

            //Load digital ID with password.
            PdfCertificate certificate = new PdfCertificate("D:\\fred.pfx", "apples");

            //Create a signature with loaded digital ID.
            PdfSignature signature = new PdfSignature(document, document.Pages[0], certificate, "DigitalSignature");
            //Set bounds to the signature.
            signature.Bounds = new System.Drawing.RectangleF(40, 40, 350, 100);

            //Load image from file.
            PdfImage image = PdfImage.FromFile("D:\\signature.png");
            //Create a font to draw text.
            PdfStandardFont font = new PdfStandardFont(PdfFontFamily.Helvetica, 15);

            //Drawing text, shape, and image into the signature appearance.
            signature.Appearance.Normal.Graphics.DrawRectangle(PdfPens.Black, PdfBrushes.White, new System.Drawing.RectangleF(50, 0, 300, 100));
            signature.Appearance.Normal.Graphics.DrawImage(image, 0, 0, 100, 100);
            signature.Appearance.Normal.Graphics.DrawString("Digitally Signed by SOHAM", font, PdfBrushes.Black, 120, 17);
            signature.Appearance.Normal.Graphics.DrawString("Reason: Cheing signature", font, PdfBrushes.Black, 120, 39);
            signature.Appearance.Normal.Graphics.DrawString("Location: Ahmedabad", font, PdfBrushes.Black, 120, 60);

            //Save the PDF document.
            document.Save("D:\\SignedAppearance.pdf");

            //Close the document.
            document.Close(true);

using Syncfusion.Pdf.Graphics;
using Syncfusion.Pdf.Parsing;
using Syncfusion.Pdf.Security;

https://www.gemboxsoftware.com/pdf/examples/c-sharp-vb-net-pdf-digital-signature/1102


public Image byteArrayToImage(byte[] bytesArr)
{
    using (MemoryStream memstr = new MemoryStream(bytesArr))
    {
        Image img = Image.FromStream(memstr);
        return img;
    }
}