PdfDocument pdf = new PdfDocument();
pdf.LoadFromFile(inputFile);

X509Certificate2 cert = new X509Certificate2(inputFile_pfx, "e-iceblue");
IPdfSignatureFormatter formatter = new PdfPKCS7Formatter(cert, false);
PdfMDPSignatureMaker pdfMDPSignatureMaker = new PdfMDPSignatureMaker(pdf, formatter);
PdfSignature signature = pdfMDPSignatureMaker.Signature;
signature.Name = "e-iceblue";
signature.ContactInfo = "028-81705109";
signature.Location = "chengdu";
signature.Reason = " this document";

PdfSignatureAppearance appearance = new PdfSignatureAppearance(signature);
appearance.NameLabel = "Signer: ";
appearance.ContactInfoLabel = "ContactInfo: ";
appearance.LocationLabel = "Loaction: ";
appearance.ReasonLabel = "Reason: ";
pdfMDPSignatureMaker.MakeSignature("signName", pdf.Pages[0], 100, 100, 250, 200, appearance);
foreach (HashAlgorithmType hashAlgorithmType in Enum.GetValues(typeof(HashAlgorithmType)))
{
    if (string.Equals(hashAlgorithmType.ToString(), "SM3", StringComparison.OrdinalIgnoreCase))
    {
        continue;
    }
    //default value of HashAlgorithm is SHA256
    formatter.Properties.HashAlgorithm = hashAlgorithmType;
    try
    {
        pdf.SaveToFile( "out.pdf", FileFormat.PDF);
    }
    catch (Exception ex)
    {
        Console.WriteLine($"error：{ex.Message}");
    }
}
pdf.Dispose();