docx4j is an open source (ASLv2) Java library for docx/pptx/xlsx, similar in concept to Open XML SDK, but with its own particular strengths including content control databinding (with OpenDoPE enhancements), XHTML import/export, PDF output, and MERGEFIELD processing. This is the .NET version of docx4j.
$ dotnet add package docx4j.NETNo README available.