dotnet/open-xml-sdk

The Open XML SDK is a library from Microsoft that lets developers read, write, and modify Word documents (.docx), Excel spreadsheets (.xlsx), and PowerPoint presentations (.pptx) using code. It works with the file format that Office has used since Office 2007, which is a compressed folder of XML files under the hood. The library gives you direct access to that underlying structure. With this SDK, a developer can do things like generate Office documents from scratch, pull content out of existing files, search and replace text, merge multiple files into one, or split a single file into parts. It can update charts and embedded data inside Word and PowerPoint files as well. These operations happen without needing Microsoft Office to be installed on the machine running the code. The library is available for .NET and is installed via NuGet, the standard package manager for .NET projects. There are a few separate packages: the core framework, a LINQ-based API for querying XML content directly, and a features package for optional extensions. Official stable releases are published to the public NuGet gallery. One thing to be aware of: this is a low-level library. It exposes the raw structure of the file format rather than providing a simple "make a table" or "set font size" interface. To use it effectively, you generally need to understand the Open XML file format specification, which is a technical document. The README points to official Microsoft documentation and Stack Overflow as the primary support resources. Several community projects build on top of this library to add simpler interfaces for specific file types, such as ClosedXML for Excel and OfficeIMO for Word.