Add enums for PDF/A-3 a and PDF/A-3 b compliance

src/UglyToad.PdfPig.Tests/Writer/PdfDocumentBuilderTests.cs

@@ -636,6 +636,8 @@
         [InlineData(PdfAStandard.A1A)]
         [InlineData(PdfAStandard.A2B)]
         [InlineData(PdfAStandard.A2A)]
+        [InlineData(PdfAStandard.A3B)]
+        [InlineData(PdfAStandard.A3A)]
         public void CanGeneratePdfAFile(PdfAStandard standard)
         {
             var builder = new PdfDocumentBuilder

src/UglyToad.PdfPig/Writer/PdfAStandard.cs

@@ -24,6 +24,14 @@
         /// <summary>
         /// Compliance with PDF/A2-A. Level A (accessible) conformance are PDF/A2-B standards in addition to features intended to improve a document's accessibility.
         /// </summary>
-        A2A = 4
+        A2A = 4,
+        /// <summary>
+        /// Compliance with PDF/A3-B. Level B (basic) conformance are PDF/A2-B standards in addition to support for embedded files
+        /// </summary>
+        A3B = 5,
+        /// <summary>
+        /// Compliance with PDF/A3-A. Level A (accessible) conformance are PDF/A3-B standards in addition to features intended to improve a document's accessibility.
+        /// </summary>
+        A3A = 6
     }
 }

src/UglyToad.PdfPig/Writer/PdfDocumentBuilder.cs

@@ -640,6 +640,11 @@ namespace UglyToad.PdfPig.Writer
                     case PdfAStandard.A2A:
                         PdfA1ARuleBuilder.Obey(catalogDictionary);
                         break;
+                    case PdfAStandard.A3B:
+                        break;
+                    case PdfAStandard.A3A:
+                        PdfA1ARuleBuilder.Obey(catalogDictionary);
+                        break;
                 }
             }
 

src/UglyToad.PdfPig/Writer/Xmp/XmpWriter.cs

@@ -147,6 +147,14 @@ namespace UglyToad.PdfPig.Writer.Xmp
                     part = 2;
                     conformance = "A";
                     break;
+                case PdfAStandard.A3A:
+                    part = 3;
+                    conformance = "A";
+                    break;
+                case PdfAStandard.A3B:
+                    part = 3;
+                    conformance = "B";
+                    break;
                 default:
                     throw new ArgumentOutOfRangeException(nameof(standard), standard, null);
             }