IText

iText is a free and open source library for creating and manipulating PDF files in Java. It was written by Bruno Lowagie, Paulo Soares, and others. As of version 5.0.0 (released Dec 7, 2009) it is distributed under the Affero General Public License version 3. Previous versions of iText (Java up to 2.1.7 and C# up to 4.1.6) were distributed under the Mozilla Public License or the LGPL. iText is also available through a proprietary license, distributed by iText Software Corp. iText® is a registered trademark by 1T3XT BVBA.

iText has been ported to the .NET Framework under the name iTextSharp. iTextSharp is written in C# and it has a separate codebase, but it is synchronized to iText releases.

Read more about IText:  Features, History, Example, Further Reading