Introduce
Free editor for PDF documents. Complete editing of PDF documents is possible with PDFedit. You can change raw pdf objects (for advanced users) or use many gui functions. Functionality can be easily extended using a scripting language (ECMAScript).

About the Project
Free (and open source) editor for manipulating PDF documents. GUI version + commandline interface.
Scripting is used to a great extent in editor and almost anything can be scripted, it is possible to create own scripts or plugins.
Target platform are operating systems of Unix type (Linux, BSD, …), we are using C++, XPDF, QT3 and QSA.
Note: QT3.x is required, editor can’t be compiled with QT4.x. In most distributions both qt3 and qt4 can be installed at once.
Editor is released under terms of GNU GPL version 2
Home Page
http://pdfedit.petricek.net/index_e.html
http://sourceforge.net/projects/pdfedit
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Google Docs supports to upload and preview PDF, It can save PDF page as image, and I notice the default name is gview, and format is png, so I think it seems to base on GSView.

GSview is a graphical interface for Ghostscript.Ghostscript is an interpreter for the PostScript page description language used by laser printers.For documents following the Adobe PostScript Document Structuring Conventions, GSview allows selected pages to be viewed or printed.GSview requires
Ghostscript.GSview is available for Windows, OS/2 and Linux.

The NightLabs PDF Viewer is an Eclipse plug-in for viewing PDF files in Eclipse-RCP-based applications. It contains Eclipse UI components (like a ‘Composite’ or an ‘Editor’) for the easy integration into your own program as well as a little stand-alone viewer application.
It bases on Sun’s pdf-renderer
You can download the demo application or the source codes here.
for more info, please visit NightLabs PDF Viewer