FFmpeg
FFmpeg is a free and open-source software project consisting of a large suite of libraries and programs for handling video, audio, and other multimedia files and streams.
iTextSharp
iText is a library for creating and manipulating PDF files in Java and .NET.
Syncfusion
Syncfusion provides the best third-party UI components for WinForms, WPF, ASP.NET Web Forms, MVC, Core, UWP, WinUI (Preview), Xamarin, JavaScript and so on...