PDF Clown - PDF Clown is an open-source general-purpose library for manipulating PDF documents through multiple abstraction layers, rigorously adhering to PDF 1.7 Specification
Document .Net - Gives you API to do everything with a document in PDF, DOCX, DOC, RTF, HTML and Text formats.
ABCpdf.NET - ABCpdf.NET is a high-profile and powerful PDF Library that delivers the best experience possible for everyone.
Wicked PDF - PDF generator (from HTML) plugin for Ruby on Rails
iTextPDF - iText offers flexible tools for PDF creation, editing and inspection.
jPDFProcess - jPDFProcess Java PDF SDK is a Java PDF Library used to create and manipulate with PDF documents that can be used to deliver customized PDF content to your users or to process incoming PDF content.