diff --git a/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfFileSpecification.cs b/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfFileSpecification.cs
index 09da5b41..6421c0a0 100644
--- a/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfFileSpecification.cs
+++ b/src/foundation/src/PDFsharp/src/PdfSharp/Pdf.Advanced/PdfFileSpecification.cs
@@ -1,4 +1,4 @@
-// PDFsharp - A .NET library for processing PDF
+// PDFsharp - A .NET library for processing PDF
 // See the LICENSE file in the solution root for more information.
 
 namespace PdfSharp.Pdf.Advanced
@@ -28,7 +28,8 @@ void Initialize()
 
             var embeddedFileDictionary = new PdfDictionary(Owner);
 
-            Owner.Internals.AddObject(_embeddedFileStream);
+            if(_embeddedFileStream.Reference is null) // 2 or more PdfFileSpecification could reference the same PdfEmbeddedFileStream, so it may not be necessary to add it again to Internals
+                Owner.Internals.AddObject(_embeddedFileStream);
             embeddedFileDictionary.Elements.SetReference(Keys.F, _embeddedFileStream.Reference ?? throw TH.InvalidOperationException_ReferenceMustNotBeNull());
             embeddedFileDictionary.Elements.SetReference(Keys.UF, _embeddedFileStream.Reference);