iText is a PDF Library or API (Application Programming Interface ) that allows the developers to generate PDF documents based on the data from database or XML file.
iText is available in Java as well as .NET (C#) and uses LDF’s many interactive features.
iText library allows the developers to add bookmarks , page numbers and watermarks.
Know more about iText Library for Creating PDF documents in C# and Java at iText product website
There is another library available in C# and Java known as Aspose for converting PDF documents to many other formats.
To convert PDF documents using C# use Aspose.PDF for .NET : http://www.aspose.com/.net/pdf-component.aspx
To convert PDF documents using Java use Aspose.PDF for Java: http://www.aspose.com/java/pdf-component.aspx