Fix ChangeDocumentType not removing VBA parts when converting to non-macro type

When changing a macro-enabled document (.docm) to a standard document (.docx)
via ChangeDocumentType(), VBA-related parts (VbaProjectPart, CustomizationPart)
were carried over to the new document type, leaving orphaned content type entries.

Add a virtual OnDocumentTypeChanged hook in TypedPackageFeatureCollection and
override it in WordprocessingDocumentFeatures to remove VBA parts when the new
type is not macro-enabled.

Fixes #618

Author: iamcymentho

src/DocumentFormat.OpenXml/Packaging/TypedPackageFeatureCollection.cs

@@ -96,6 +96,7 @@ void IDocumentTypeFeature<TDocumentType>.ChangeDocumentType(TDocumentType newTyp
         try
         {
             Package.ChangeDocumentTypeInternal(CreateMainPart());
+            OnDocumentTypeChanged(newType);
         }
         catch (OpenXmlPackageException e)
         {
@@ -116,5 +117,13 @@ void IDocumentTypeFeature<TDocumentType>.ChangeDocumentType(TDocumentType newTyp
 
     protected abstract TMainPart CreateMainPart();
 
+    /// <summary>
+    /// Called after the document type has been changed. Subclasses can override to perform
+    /// cleanup such as removing parts that are not valid for the new document type.
+    /// </summary>
+    protected virtual void OnDocumentTypeChanged(TDocumentType newType)
+    {
+    }
+
     bool IKnownDataPartFeature.IsKnown(string relationshipId) => false;
 }

src/DocumentFormat.OpenXml/Packaging/WordprocessingDocument.cs

@@ -582,6 +582,21 @@ public WordprocessingDocumentFeatures(OpenXmlPackage package)
                 "application/vnd.ms-word.template.macroEnabledTemplate.main+xml" => WordprocessingDocumentType.MacroEnabledTemplate,
                 _ => default,
             };
+
+            protected override void OnDocumentTypeChanged(WordprocessingDocumentType newType)
+            {
+                if (newType is WordprocessingDocumentType.MacroEnabledDocument
+                    or WordprocessingDocumentType.MacroEnabledTemplate)
+                {
+                    return;
+                }
+
+                if (MainPart is { } mainPart)
+                {
+                    mainPart.DeletePartsOfType<VbaProjectPart>();
+                    mainPart.DeletePartsOfType<CustomizationPart>();
+                }
+            }
         }
     }
 }

test/DocumentFormat.OpenXml.Tests/DocxTests01.cs

@@ -361,6 +361,53 @@ public void W039_ChangeDocumentType()
             }
         }
 
+        [Fact]
+        public void ChangeDocumentType_MacroEnabledToDocument_RemovesVbaParts()
+        {
+            using var stream = new MemoryStream();
+
+            // Create a macro-enabled document with a VbaProjectPart
+            using (var doc = WordprocessingDocument.Create(stream, WordprocessingDocumentType.MacroEnabledDocument))
+            {
+                var mainPart = doc.AddMainDocumentPart();
+                mainPart.Document = new W.Document(new W.Body(new W.Paragraph(new W.Run(new W.Text("Test")))));
+
+                // Add a VbaProjectPart (the part that causes the issue)
+                mainPart.AddNewPart<VbaProjectPart>();
+
+                Assert.NotNull(mainPart.VbaProjectPart);
+                Assert.Equal(WordprocessingDocumentType.MacroEnabledDocument, doc.DocumentType);
+            }
+
+            // Re-open and change type to a standard document
+            stream.Position = 0;
+
+            using (var doc = WordprocessingDocument.Open(stream, true))
+            {
+                Assert.Equal(WordprocessingDocumentType.MacroEnabledDocument, doc.DocumentType);
+                Assert.NotNull(doc.MainDocumentPart.VbaProjectPart);
+
+                doc.ChangeDocumentType(WordprocessingDocumentType.Document);
+
+                Assert.Equal(WordprocessingDocumentType.Document, doc.DocumentType);
+
+                // After changing to a non-macro type, VbaProjectPart should be removed
+                Assert.Null(doc.MainDocumentPart.VbaProjectPart);
+            }
+
+            // Re-open and verify the VBA content type is not present in the package
+            stream.Position = 0;
+
+            using (var package = Package.Open(stream, FileMode.Open, FileAccess.Read))
+            {
+                var contentTypes = package.GetParts()
+                    .Select(p => p.ContentType)
+                    .ToList();
+
+                Assert.DoesNotContain("application/vnd.ms-office.vbaProject", contentTypes);
+            }
+        }
+
         [Fact]
         public void W038_DocxCreation_Package()
         {