263843: Added code example for Retrieve Certificate Policy from PDF document

Digital Signature/Retrieve-Certificate-Policy-from-PDF/.NET/Retrieve-Certificate-Policy-from-PDF.slnx

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+<Solution>
+  <Project Path="Retrieve-Certificate-Policy-from-PDF/Retrieve-Certificate-Policy-from-PDF.csproj" />
+</Solution>

Digital Signature/Retrieve-Certificate-Policy-from-PDF/.NET/Retrieve-Certificate-Policy-from-PDF/Program.cs

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+using Syncfusion.Pdf.Parsing;
+using Syncfusion.Pdf.Security;
+using System.Security.Cryptography.X509Certificates;
+
+// Load signed PDF
+using (PdfLoadedDocument document = new PdfLoadedDocument(Path.GetFullPath(@"Data/Input.pdf")))
+{
+    // Get the PDF form
+    PdfLoadedForm form = document.Form;
+    if (form != null && form.Fields != null && form.Fields.Count > 0)
+    {
+        foreach (PdfLoadedField field in form.Fields)
+        {
+            // Check for signature field
+            if (field is PdfLoadedSignatureField signatureField && signatureField.IsSigned)
+            {
+                Console.WriteLine($"Signature Field: {signatureField.Name}");
+                // Validate signature
+                PdfSignatureValidationResult result = signatureField.ValidateSignature();
+                if (result?.Certificates != null && result.Certificates.Count > 0)
+                {
+                    X509Certificate2 certificate = result.Certificates[0];
+                    Console.WriteLine("Issuer: " + certificate.Issuer);
+                    Console.WriteLine("Subject: " + certificate.Subject);
+                    string policyId = GetCertificatePolicyOID(certificate);
+
+                    if (!string.IsNullOrEmpty(policyId))
+                    {
+                        Console.WriteLine($"Policy OID: {policyId}");
+                    }
+                    else
+                    {
+                        Console.WriteLine("❌ Certificate policy not found.");
+                    }
+                    Console.WriteLine("-----------------------------------");
+                }
+            }
+        }
+    }
+}
+
+// Extract Certificate Policy OID (2.5.29.32)
+string GetCertificatePolicyOID(X509Certificate2 certificate)
+{
+    foreach (X509Extension extension in certificate.Extensions)
+    {
+        if (extension?.Oid?.Value == "2.5.29.32")
+        {
+            string formatted = extension.Format(true);
+            // Example format contains: "Policy Identifier=OID"
+            return ExtractPolicyID(formatted);
+        }
+    }
+    return null;
+}
+
+// Extracts Policy Identifier from formatted string
+string ExtractPolicyID(string policyText)
+{
+    if (string.IsNullOrEmpty(policyText))
+        return null;
+    const string keyword = "Policy Identifier=";
+    int index = policyText.IndexOf(keyword, StringComparison.OrdinalIgnoreCase);
+    if (index < 0)
+        return null;
+    index += keyword.Length;
+    int endIndex = policyText.IndexOf(",", index);
+    string rawOid;
+    if (endIndex > index)
+        rawOid = policyText.Substring(index, endIndex - index);
+    else
+        rawOid = policyText.Substring(index);
+    // Clean unwanted characters
+    return CleanOID(rawOid);
+}
+
+string CleanOID(string oid)
+{
+    if (string.IsNullOrEmpty(oid))
+        return null;
+    // Remove line breaks, tabs, spaces
+    oid = oid.Replace("\r", "")
+             .Replace("\n", "")
+             .Replace("\t", "")
+             .Trim();
+    // Remove anything after invalid characters like '['
+    int index = oid.IndexOfAny(new char[] { '[', ' ' });
+    if (index > 0)
+        oid = oid.Substring(0, index);
+    return oid.Trim();
+}

Digital Signature/Retrieve-Certificate-Policy-from-PDF/.NET/Retrieve-Certificate-Policy-from-PDF/Retrieve-Certificate-Policy-from-PDF.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <RootNamespace>Retrieve_Certificate_Policy_from_PDF</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Syncfusion.Pdf.Net.Core" Version="*" />
+  </ItemGroup>
+
+</Project>