[3.4.0]

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

[3.3.0]

Added

• Added DocumentFormat.OpenXml.Office.SpreadSheetML.Y2024.WorkbookCompatibilityVersion namespace

Fixed

• Performance of .ToFlatOpc(...) has been greatly improved for large parts (#1863)

Thanks to the following for their contributions:

@QuocDatHoang

[3.2.0]

Added

• Added DocumentFormat.OpenXml.Office.SpreadSheetML.Y2022.PivotRichData namespace
• Added DocumentFormat.OpenXml.Office.SpreadSheetML.Y2024.PivotDynamicArrays namespace

Changed

• Updated Nuget badge on README

Fixed

• Fixed issue where a disposed object (DeflateStream) cannot be accessed after recovering from malformed url (#1802)
• Fixed issue with relationships not being created when cloning Flat OPC (#1814)
• Fixed issue with corrupt files remaining locked after attempting to open with WordprocessingDocument.Open (#1681)
• Fixed issue with changes not applied after .Save() (#1771)
• Fixed AddWorkbookPart throws exception if no main part is available (#1745)
• Fixed issue with base classes not included with LINQ generation (#1838)

Thanks to the following for their contributions:

@WeihanLi

[3.1.1]

Fixed

• Updated System.IO.Packaging and other dependencies (#1794, #1795, #1796, #1782, #1808)
• Fixed add c16:uniqueId to several chart complex types (#1762)
• Fixed rather than in the documentation comments (#1775)

[3.1.0]

Added

• Added DocumentFormat.OpenXml.Office.SpreadSheetML.Y2024.PivotAutoRefresh namespace
• Added DocumentFormat.OpenXml.Office.SpreadSheetML.Y2024.PivotDynamicArrays namespace
• Added DocumentFormat.OpenXml.Office.SpreadSheetML.Y2023.DataSourceVersioning namespace
• Added DocumentFormat.OpenXml.Office.SpreadSheetML.Y2023.ExternalCodeService namespace
• Added DocumentFormat.OpenXml.Office.SpreadSheetML.Y2023.MsForms namespace
• Added DocumentFormat.OpenXml.Office.SpreadSheetML.Y2023.Pivot2023Calculation namespace

Fixed

• Fixed issue where OpenXmlUnknownElement is returned instead of CommentPropertiesExtension (#1751)
• Fixed issue where OpenXmlWriter is unable to write SharedStringTablePart (#1755)

[3.0.2]

Fixed

• Fixed issue where temp files were shareable and not deleted on close (#1658)

[3.0.1]

Fixed

• Fixed issue where document type would not be correct unless content type was checked first (#1625)
• Added check to only seek on packages where it is supported (#1644)
• If a malformed URI is encountered, the exception is now the same as v2.x (OpenXmlPackageException with an inner UriFormatException) (#1644)

[3.0.0]

Added

• Packages can now be saved on .NET Core and .NET 5+ if constructed with a path or stream (#1307).
• Packages can now support malformed URIs (such as relationships with a URI such as mailto:person@)
• Introduce equality comparers for OpenXmlElement (#1476)
• IFeatureCollection can now be enumerated and has a helpful debug view to see what features are registered (#1452)
• Add mime types to part creation (#1488)
• DocumentFormat.OpenXml.Office.PowerPoint.Y2023.M02.Main namespace
• DocumentFormat.OpenXml.Office.PowerPoint.Y2022.M03.Main namespace
• DocumentFormat.OpenXml.Office.SpreadSheetML.Y2021.ExtLinks2021 namespace

Changed

• When validation finds incorrect part, it will now include the relationship type rather than a class name
• IDisposableFeature is now a part of the framework package and is available by default on a package or part.

Breaking Changes

• .NET Standard 1.3 is no longer a supported platform. .NET Standard 2.0 is the lowest .NET Standard supported.
• Core infrastructure is now contained in a new package DocumentFormat.OpenXml.Framework. Typed classes are still in DocumentFormat.OpenXml. This means that you may reference DocumentFormat.OpenXml and still compile the same types, but if you want a smaller package, you may rely on just the framework package.
• Changed type of OpenXmlPackage.Package to DocumentFormat.OpenXml.Packaging.IPackage instead of System.IO.Packaging.Package with a similar API surface
• EnumValue<T> now is used to box a struct rather than a System.Enum. This allows us to enable behavior on it without resorting to reflection
• Methods on parts to add child parts (i.e. AddImagePart) are now implemented as extension methods off of a new marker interface ISupportedRelationship<T>
• Part type info enums (i.e. ImagePartType) is no longer an enum, but a static class to expose well-known part types as structs. Now any method to define a new content-type/extension pair can be called with the new PartTypeInfo struct that will contain the necessary information.
• OpenXmlPackage.CanSave is now an instance property (#1307)
• Removed OpenXmlSettings.RelationshipErrorHandlerFactory and associated types and replaced with a built-in mechanism to enable this
• IdPartPair is now a readonly struct rather than a class
• Renamed PartExtensionProvider to IPartExtensionFeature and reduced its surface area to only two methods (instead of a full Dictionary<,>). The property to access this off of OpenXmlPackage has been removed, but may be accessed via Features.Get<IPartExtensionFeature>() if needed.
• OpenXmlPart/OpenXmlContainer/OpenXmlPackage and derived types now have internal constructors (these had internal abstract methods so most likely weren't subclassed externally)
• OpenXmlElementList is now a struct that implements IEnumerable<OpenXmlElement> and IReadOnlyList<OpenXmlElement> where available (#1429)
• Individual implementations of OpenXmlPartReader are available now for each package type (i.e. WordprocessingDocumentPartReader, SpreadsheetDocumentPartReader, PresentationDocumentPartReader), and the previous TypedOpenXmlPartReader has been removed. (#1403)
• Reduced unnecessary target frameworks for packages besides DocumentFormat.OpenXml.Framework (#1471)
• Changed some spelling issues for property names (#1463, #1444)
• Model3D now represents the modified xml element tag name am3d.model3d (Previously am3d.model3D)
• Removed DocumentFormat.OpenXml.Office.SpreadSheetML.Y2022.PivotRichData.PivotCacheHasRichValuePivotCacheRichInfo
• Removed DocumentFormat.OpenXml.Office.SpreadSheetML.Y2022.PivotRichData.RichDataPivotCacheGuid
• Removed unused SchemaAttrAttribute (#1316)
• Removed unused ChildElementInfoAttribute (#1316)
• Removed OpenXmlSimpleType.TextValue. This property was never meant to be used externally (#1316)
• Removed obsolete validation logic from v1 of the SDK (#1316)
• Removed obsoleted methods from 2.x (#1316)
• Removed mutable properties on OpenXmlAttribute and marked as readonly (#1282)
• Removed OpenXmlPackage.Close in favor of Dispose (#1373)
• Removed OpenXmlPackage.SaveAs in favor of Clone (#1376)

[3.0.0-beta3]

Added

• Introduce equality comparers for OpenXmlElement (#1476)
• IFeatureCollection can now be enumerated and has a helpful debug view to see what features are registered (#1452)
• Add mime types to part creation (#1488)

Breaking changes

• Reduced unnecessary target frameworks for packages besides DocumentFormat.OpenXml.Framework (#1471)
• Changed some spelling issues for property names (#1463, #1444)

[v3.0.0-beta2]

Breaking Changes

• OpenXmlElementList is now a struct that implements IEnumerable<OpenXmlElement> and IReadOnlyList<OpenXmlElement> (where available)
• Individual implementations of OpenXmlPartReader are available now for each package type (i.e. WordprocessingDocumentPartReader, SpreadsheetDocumentPartReader, PresentationDocumentPartReader), and the previous TypedOpenXmlPartReader has been removed.