ConcatPDF is the tool to concatenate PDF files. It can concatenate, extract, encrypt, decrypt, configure PDF files, convert image files to PDF. GUI version and CUI version are both available.
iText.NET is iText porting on .NET Framework by J#. This library allows you to generate PDF, (X)HTML, XML, RTF files on Microsoft.NET Framework including ASP.NET.
Free HTML to PDF Converter for C# .NET and ASP.NET MVC
HiQPdf Library for C# .NET offers you a modern, simple, fast, flexible and powerful tool to create complex and stylish PDF documents in your applications with just a few lines of code.
Using the high quality HTML to PDF conversion engine you can easily design a document in HTML with CSS3, JavaScript, SVG or Canvas and then convert it to PDF preserving the exact content and style.