NetOffice is a great .NET library which can be used to develop solutions for Microsoft Office apps. The library supports automation and extension scenarios.
Automation
Use the NetOffice library to automate Microsoft Office apps. You can generate Office documents, transform and print them.
You can automate repetitive actions like adding signatures and pictures to Word documents, or generating Excel spreadsheets which must use the same Excel formulas you would manually create.
Extensions
NetOffice has first class support for Microsoft Office Add-ins – rich extensions which can modify user interface inside Office application and allow users to access complex features.
NetOffice add-ins are written in managed .NET code so the development is easy, productive and you can debug them from Visual Studio.
NetOffice documentation is available at https://netoffice.io/ and you can join the development community on GitHub at https://github.com/NetOfficeFw