Questions about: open-source

I would suggest you take a look at PDFcrop. If you wish to crop a pdf with left, top, right and bottom margins of 5, 10, 20, and 30 pt (points), then run pdfcrop --margins '5 10 20 30' input. pdf output
The terms free software and open source software do mean different things, though the categories of software they refer to are almost exactly the same. Free software is defined in terms of freedom (not price), and is not the same thing as freeware. T