If you have a PDF document and want to crop it, e.g. because you have too large borders and/or it is skewed or there are actually two pages in each page, this software may help.
Briss comes in Java and is good for cropping and deskewing pages: http://briss.sourceforge.net/. This works fully automatically for single pages and is very nice. As it's written in Java, it works on Mac, Windows and Linux just the same. I will keep this for all my image pdf cropping needs. To split double pages I would first deskew and crop automatically in the first run and then save. That file I recommend to use for a second run and there crop the pages into two parts manually.
Unpaper (http://unpaper.berlios.de/) is a CLI tool for the job, which supports double pages, which briss doesn't yet seem to support. But it requires the PDFs to be split into .pbm , .pgm or .ppm first.
e.g. convert ./unpaper -l double -s a5 00000001.pgm 00000001a.pgm. But in my experience it didn't work at all...
And this helps for OCR: http://blog.konradvoelkel.de/2010/01/linux-ocr-and-pdf-problem-solved/