PDF Mod is a simple application for modifying PDF documents.
The latest release is 0.9.1 (release notes) released March 3, 2011
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PDF Mod is built on top of Poppler (for rendering), PDFsharp (for manipulating/saving), Mono, Gtk#, Cairo, and Banshee's Hyena library. All told it is about 2,600 lines of C#. 15 developers have contributed to the project. It includes full user-documentation and has been translated into 26 languages by 39 translators.