Sometimes you might have scanned all pages of a PDF a bit larger than necessary. The PDF Scissors tool makes it extremely easy to crop all pages of a PDF file. You can also crop odd pages and even pages differently or just crop one or few pages.
The tool is written in Java and can be run directly from the website here, by clicking the Start button on it. This downloads a
.jnlp file which you can run directly. If you cannot run it, see this post. Running it downloads the PDF Scissors tool and runs it.
Open the PDF you want to crop and the tool nicely stacks all the pages, so you can clearly see the bounding box of actual content in those pages. Just draw the crop rectangle, adjust it as much as you want and press the Save button to save it to a new PDF file. Bingo!