dotnet/wpf · error · XpsPackagingException

PackagePart URI does not correspond to a FixedDocument.

Error message

PackagePart URI does not correspond to a FixedDocument.

What it means

XpsPackagingException thrown by AddDocumentToCache when the part at the document URI exists in the package but its validated content type is not FixedDocumentContentType. The FixedDocumentSequence referenced a part that is present but is not a FixedDocument. The library throws to prevent building a reader for the wrong part type.

Solutions

1. Open the package as a zip and confirm the target part's entry in [Content_Types].xml maps to the FixedDocument content type (application/vnd.ms-package.xps-fixeddocument).
2. Regenerate the XPS from the original application rather than manually re-zipping, which can drop correct content-type mappings.
3. Verify the FixedDocumentSequence relationship targets the .fdoc/FixedDocument part, not a page or resource.
4. If authoring packages, use XpsDocument/XpsFixedDocumentSequenceWriter APIs so content types are set automatically.
5. Validate input files with an XPS conformance checker before processing.

Example fix

// before
// package manually re-zipped: Documents/1/FixedDoc.fdoc content type lost
// after
// Repack so [Content_Types].xml contains:
// <Default Extension="fdoc" ContentType="application/vnd.ms-package.xps-fixeddocument"/>
// or rebuild via:
using (XpsDocument doc = new XpsDocument(outPath, FileAccess.ReadWrite))
{
    IXpsFixedDocumentSequenceWriter w = doc.AddFixedDocumentSequence();
    // ... write documents through the API
    w.Commit();
}

// Before reading: confirm the target part's content type is FixedDocument
Uri partUri = PackUriHelper.ResolvePartUri(seqUri, rel.TargetUri);
PackagePart part = package.GetPart(partUri);
if (!part.ContentType.Equals("application/vnd.ms-package.xps-fixeddocument", StringComparison.OrdinalIgnoreCase))
    throw new InvalidDataException($"Part {partUri} is {part.ContentType}, not a FixedDocument");

static bool IsFixedDocumentPart(PackagePart part) =>
    part != null && string.Equals(part.ContentType,
        "application/vnd.ms-package.xps-fixeddocument", StringComparison.OrdinalIgnoreCase);

try
{
    var reader = seqReader.GetFixedDocumentAt(i);
}
catch (XpsPackagingException ex) when (ex.Message.Contains("FixedDocument"))
{
    // skip/flag malformed document entry
    log.Warn($"Document {i} has wrong content type: {ex.Message}");
}

When it happens

Trigger: Calling document-reading APIs on an XPS package where the FixedDocumentSequence's document relationship targets a part whose ContentType is not the FixedDocument MIME type — e.g. the URI points to a FixedPage, a thumbnail, or a renamed custom part.

Common situations: XPS files produced by nonconforming generators that mislabel content types; packages where [Content_Types].xml entries were edited or lost; a FixedDocument part renamed with an extension that changed its inferred type; mixing .oxps/.xps content-type conventions.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

• ' ' ContentType is not valid.
• Can only countersign parts with Digital Signature…
• Document PackagePart URI is not valid.
• Only writers can call this method.
• Package must contain an XPS PackagePart.

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/7cbbda21baebab3f. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/ReachFramework/Packaging/XpsFixedDocumentSequenceReaderWriter.cs:619

        private
        IXpsFixedDocumentReader
        AddDocumentToCache(Uri documentUri)
        {
            //
            // Retrieve the requested part from the package
            //
            PackagePart documentPart = CurrentXpsManager.GetPart(documentUri);
            if (documentPart == null)
            {
                 throw new XpsPackagingException(SR.ReachPackaging_PartNotFound);
            }

            //
            // If the part is not a fixed document then throw an exception
            //
            if (!documentPart.ValidatedContentType().AreTypeAndSubTypeEqual(XpsS0Markup.FixedDocumentContentType))
            {
                throw new XpsPackagingException(SR.ReachPackaging_NotAFixedDocument);
            }

            //
            // Create the reader/writer for the part
            //
            IXpsFixedDocumentReader  fixedDocument = new XpsFixedDocumentReaderWriter(CurrentXpsManager, null, documentPart, _documentCache.Count+1);

            //
            // Cache the new reader/writer for later
            //
            _documentCache.Add( fixedDocument );
            return fixedDocument;
        }


        #endregion Private methods

        #region Private data

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