iText PDF

iText is a library that allows you to generate PDF files on the fly.

iText is an ideal library for developers looking to enhance web- and other applications with dynamic PDF document generation and/or manipulation. iText is not an end-user tool. Typically you won't use it on your Desktop as you would use Acrobat or any other PDF application. Rather, you'll build iText into your own applications so that you can automate the PDF creation and manipulation process.

You can use iText to:

• Serve PDF to a browser
• Generate dynamic documents from XML files or databases
• Use PDF's many interactive features
• Add bookmarks, page numbers, watermarks, etc.
• Split, concatenate, and manipulate PDF pages
• Automate filling out of PDF forms
• Add digital signatures to a PDF file
• And much more...

www.itextpdf.com

iTextSharp

iTextSharp is a library that allows you to generate PDF files on the fly. iTextSharp is a port of the iText, a free Java-Pdf library.

http://itextsharp.sourceforge.net/

Xpdf

Xpdf is an open source PDF viewer for the X Window System and Motif.Xpdf runs on practically any Unix-like operating system. Xpdf can decode LZW and read encrypted PDFs. The official version obeys the DRM restrictions of PDF files, which may prevent copying, printing, or converting some PDF files.There are patches which make Xpdf ignore these DRM restrictions.
Xpdf includes several programs that don't require the X Window System, including programs which extract images from PDF files or convert PDF to PostScript or text. These programs run on DOS, Windows as well as Linux and Unix.

http://www.foolabs.com/xpdf/