optimizes PDF/DJVU files for mobile e-readers (e.g. the Kindle) and smartphones. It works well on multi-column PDF/DJVU files. K2pdfopt is open source.
HOW TO USE K2PDFOPT:
No install is required and no extra files or packages are necessary to run k2pdfopt. Just drag and drop your PDF/DJVU file icon onto the k2pdfopt icon to convert it. You will be prompted for conversion options (as of v1.16). Press <Enter> to convert the file using the default settings. A new PDF file with _k2opt at the end of the name will be created. The output file is optimized for viewing on Kindles and other mobile readers with 6-inch screens (if the settings are not customized). Or drop a folder full of PDF/DJVU files onto the k2pdfopt icon to batch process. You can even drop a folder full of bitmap images to have them converted into a single PDF as if they were pages of a PDF file.
Now it has built-in GUI for Windows version:
how to: http://willus.com/archive/k2pdfopt/help/
can be used on Windows, Linux and OS X