Kdan PDF Reader - The All-in-One Document Expert Designed for the Increasingly-mobile Workplace.
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
iText - iText is an intuitive and refined text editor with word processing completely rewritten in Cocoa...
Document .Net - Gives you API to do everything with a document in PDF, DOCX, DOC, RTF, HTML and Text formats.
Apache PDFBox - The Apache PDFBox™ library is an open source Java tool for working with PDF documents.
PDFSharp - Office & Productivity and Development