iTextSharp

iTextSharp is a port of the iText, a free Java-Pdf library.

Technical Requirements

To use these classes you should be acquainted with Microsoft C# programming.
You'll also need the following Software:

The Microsoft .Net Framework 1.1:
Adobe Acrobat Reader from Adobe Systems Incorporated:

Documentation

For more info on the use of iText, you can consult the iText documentation (JAVA).
You can also find some real iTextSharp examples based on the old iText tutorial and some online demo examples here; these old tutorial examples were converted by a Chinese developer. He keeps a Chinese blog with lots of demo material.
A French version based on the old tutorial (translated by Joël Marty) is available here (Word document).
Note that some of the example won't work with the most recent version of iTextSharp.