Why? The document was fine on the PC that created it. Why doesn\'t Word keep the same parameters, or at least import the settings the document was created with into my copy of Word?
The problem is that different printers can print to different distances from the edge of the page. Some modern photo-capable printers can print right up to the edges of the page, but most laser printers and inkjets leave a margin of 0.2", 0.4", or more. Chances are that the document was laid out by someone whose printer can get closer to the edges of the paper than your printer can. You may also find that this occurs with a document you create yourself if you switch from one local (or network) printer to another that uses wider margins.
The fix is easy enough: if Word offers you a Fix button, click it to fix the problem automatically. Otherwise, choose File » Page Setup, click the Margins tab, and adjust the offending margin or margins. Unless you're creating intricate layouts, it's usually a good idea to leave large margins on your documents anyway; they look less crowded, and people can scribble notes on them more easily.
Handle Swelling of the Right Margin
I printed the first few pages of the new sales report we've been working on, and the right margin is about two inches fatter than it should be. The bottom margin is bigger too.
It sounds as though the document contains tracked changes (or comments), the view is showing "Final with markup" or "Original with markup" rather than "Final," and the pages you printed don't have any tracked changes or markup on them. Word is reserving space in the right and bottom margins for the change balloons and notes, even though there aren't any on these pages.
To fix this problem, either get rid of the tracked changes (accept them or reject them, as appropriate) or switch the view to "Final" in the "Display for review" drop-down list on the Reviewing toolbar.