dotnet/wpf · error · XpsPackagingException

ReachPackaging_NotAFixedDocumentSequence

Error message

ReachPackaging_NotAFixedDocumentSequence

What it means

GetFixedDocumentSequence throws this XpsPackagingException when the part referenced as the root does not correspond to a FixedDocumentSequence — the starting part's content/URI resolves to something other than an .fdseq root, so a FixedDocumentSequence cannot be produced from it.

Solutions

1. Ensure the package's starting part has the FixedDocumentSequence content type (.fdseq) before calling GetFixedDocumentSequence
2. Call the appropriate reader method (GetFixedDocument / page APIs) for packages whose root is not a FixedDocumentSequence
3. Catch XpsPackagingException and inspect the starting part content type to route to the right reader

When it happens

Trigger: Thrown at src/Microsoft.DotNet.Wpf/src/ReachFramework/Packaging/XpsDocument.cs:625 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/7f2994e28a272945. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/ReachFramework/Packaging/XpsDocument.cs:625

            ParserContext parserContext = new ParserContext
            {
                BaseUri = PackUriHelper.Create(Uri, CurrentXpsManager.StartingPart.Uri)
            };

            Uri packageUri = PackUriHelper.GetPackageUri(parserContext.BaseUri);

            Uri previousPackageUri = XpsLoadingContext.ActivePackageUri;
            
            // Establish XPS package context so that ambient-check sinks
            // (BitmapImage, BitmapDecoder, ColorContext, FontSource, PixelShader)
            // see the correct package origin during .fdseq parsing.
            XpsLoadingContext.ActivePackageUri = packageUri;
            try
            {
                object fixedObject = XamlReader.Load(CurrentXpsManager.StartingPart.GetStream(), parserContext, useRestrictiveXamlReader: true);
                if (!(fixedObject is FixedDocumentSequence))
                {
                     throw new XpsPackagingException(SR.ReachPackaging_NotAFixedDocumentSequence);
                }

                return fixedObject as FixedDocumentSequence;
            }
            finally
            {
                XpsLoadingContext.ActivePackageUri = previousPackageUri;
            }
        }

        /// <summary>
        /// This method commits the changes of the package and closes it.
        /// Further changes after a commit will cause an exception to be
        /// thrown.
        /// </summary>
        internal
        override
        void

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