I need help.
I am writing a PDF digitally signed API application and am using PdfStamper. But when I run it, I get an error and I can't find the cause of the error. The error displayed is: 'Object reference not set to an instance of an object'
Help me! Thank you!
Below is the code that I wrote:
public void doSign(String src, String dest, float llx, float lly, float urx, float ury, int NumPage, String FieldName)
{
try
{
PdfReader reader = new PdfReader(src);
FileStream os = new FileStream(dest, FileMode.Create);
PdfStamper stamper = PdfStamper.CreateSignature(reader, os, '\0');
Byte[] CertificateValue = SignAPI.GetCertificate();
ICollection<X509Certificate> chain = this.GetCertificateChain(CertificateValue);
PdfSignatureAppearance appearance = stamper.SignatureAppearance;
X509CertificateParser cp = new X509CertificateParser();
appearance.Certificate = cp.ReadCertificate(CertificateValue);
appearance.SetVisibleSignature(new Rectangle(llx, lly, urx, ury), NumPage, FieldName);
byte[] hash = this.CreateHash(appearance, chain);
byte[] exSignature = this.MobilePKIHash(hash);
this.AddSignature(appearance, exSignature);
}
catch(Exception e)
{
File.AppendAllText(Directory.GetCurrentDirectory() + "/Log/Log.txt", "Ngày " + DateTime.Now.ToString("dd-MM-yyyy HH:mm:ss +0700") + ": Thực hiện Ký số thất bại! Lỗi --> " + e.ToString() + Environment.NewLine);
}
}
