Recently I received one PDF document with huge margins – the text itself was located in the middle of the page and its size was about 1/3 of the page. As you can imagine, reading it on-screen is really painful; also you cannot print only part of the page in Acrobat reader, which is IMHO a big omission on the Adobe’s side. Well, I thought that cropping the page would really solve the trouble, but it took me rather much time to find something affordable, simple, and inexpensive (maybe even free – who knows?) – A-PDF Page Crop. You can crop pages both visually in editor, or from command line (useful only if you have lots of similar documents; I was not trying that option) – and it does its job well. Trial version puts its mark on the front page, and that can be removed by getting a licensed version. Nothing more to say – the tool does what it is made for. That company also has many other PDF-related utilities.