Digitally Sign a PDF or Other Files

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Demonstrates how to digitally sign a PDF file (and verify it) in C#

// Converts any kind of file into an S/MIME message with
// a detached (clear-text) signature.
private void CreateSigned_Click(object sender, System.EventArgs e)
{
	Chilkat.Mime mime = new Chilkat.Mime();
	
	
	mime.UnlockComponent("UnlockCode");
	mime.SetBodyFromPlainText("This is a message containing a PDF file.");
	mime.AppendPartFromFile("sample.pdf");
	mime.SaveMime("unsigned.txt");

	// Locate a certificate in the Current User Store (in the registry)
	// There are many different ways of locating and using certificates
	// using Cert, CertStore and CreateCS.
	Chilkat.CreateCS ccs = new Chilkat.CreateCS();
	Chilkat.CertStore certStore = ccs.OpenCurrentUserStore();
	Chilkat.Cert cert = certStore.FindCertForEmail("matt@chilkatsoft.com");

	// Use the certificate for signing.
	mime.AddDetachedSignature(cert);
	mime.SaveMime("signed.txt");

}

private void VerifySigned_Click(object sender, System.EventArgs e)
{
	Chilkat.Mime mime = new Chilkat.Mime();
	
	
	mime.UnlockComponent("UnlockCode");

	// Load the signed MIME
	mime.LoadMimeFile("signed.txt");

	// Unwrap the security (verify all signatures and decrypt, if necessary)
	bool verified = mime.UnwrapSecurity();
	if (verified) 
	{
		// Show the certificate that signed the message.
		if (mime.NumSignerCerts > 0)
		{
			Chilkat.Cert cert = mime.GetSignerCert(0);
			MessageBox.Show(cert.SubjectDN);
		}

		// Extract the PDF and save it.
		Chilkat.Mime pdfPart = mime.GetPart(1);
		pdfPart.SaveBody("out.pdf");
	}
	else
	{
		MessageBox.Show(mime.LastError);
	}


}