iTextSharp
iTextSharp is a .NET library for creating and manipulating PDF documents programmatically. It allows developers to generate PDFs from scratch, add text, images, tables, and forms, as well as modify existing PDF files. Originally a port of the Java-based iText library, it provides extensive functionality for PDF generation and processing in C# and other .NET languages.
Developers should learn iTextSharp when building applications that require dynamic PDF generation, such as report generation, invoice creation, or document automation in .NET environments. It is particularly useful for scenarios where PDFs need to be created on-the-fly from data sources, or when existing PDFs require modifications like adding watermarks, merging files, or extracting content.