Sourced from DocumentFormat.OpenXml's releases.

3.5.1

Added

• Added DocumentFormat.OpenXml.Office2016.Drawing.ChartDrawing.Offset class
• Added Version attribute to DocumentFormat.OpenXml.Office2016.Drawing.ChartDrawing.ChartSpace
• Added FeatureList attribute to DocumentFormat.OpenXml.Office2016.Drawing.ChartDrawing.ChartSpace
• Added FalbackImg attribute to DocumentFormat.OpenXml.Office2016.Drawing.ChartDrawing.ChartSpace
• Added DocumentFormat.OpenXml.Office2016.Drawing.ChartDrawing.ExtensionDropMode enum

3.4.1

Added

• Added MediaDataPartType.Mp4 to support MP4 video media parts in presentations and documents (#​1866)
• Updated bundled Open XML schemas to the Q3 2025 Office release, enabling newer document and presentation features (#​1963)

Changed

• Reduced JIT and AOT size and improved document load performance by removing the generic builder pattern from element metadata creation (#​1842, #​1843)
• Optimized FromChunkedBase64String to significantly reduce allocations and improve throughput when decoding chunked base64 content (≈2.4× faster, ≈70% less memory) (#​1868)

Fixed

• Switched to XmlDOMTextWriter instead of XmlWriter.Create to correctly handle serialization of certain XML content (#​1869, #​1961)
• Added a clear error when attempting to open encrypted documents that the SDK cannot process (#​1635, #​1969)
• Improved exception messages when required package parts are missing by including the name of the missing part (#​1971, #​1974)

Documentation

• Clarified the README SDK description and simplified the note on 3.0.0 breaking changes (#​1858)
• Documented that disposing a package with AutoSave set to false does not persist changes (#​1873)
• Removed the PowerPoint modern comments sample, which now lives on learn.microsoft.com (#​1861)

Thanks to the following for their contributions:

@​QuocDatHoang
@​Varorbc

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