Krop

Krop is used for spliting pages in a pdf file into sub-pages, doing this may help you crop the pages of a PDF file to fit the limited screen size of devices such as eReaders. One of the interesting features of Krop is that it has the option of automatic selection via Trim Margins button. Also, while cropping you can apply it on all pages, even/odd page, or a individual page. Page exeption is also supported.