PDFTron is now Apryse. Same great products, new name.

C# .NET PDF library

PDFTron offers a high-quality, feature-rich and industry-strength PDF SDK (with WPF/WinForms support) for the most demanding and diverse applications. Use PDFTron to build stand-alone, cross-platform, and reliable commercial applications that can read, write, edit, print and display PDF documents. PDFTron's C# PDF library is trusted by thousands of innovative startups, governments, and Fortune 500 businesses (see customers). PDFTron technology is built from the ground up and is not dependent on any external third-party open-source software.