A family of Microsoft word processing software products for creating web, email, and print documents.
Although Word 2007 and 2010 do have native support for creating PDFs, no version of Word until Word 2013 can open or edit them. For that you need the free Adobe Reader; in the unlikely event that you don't have it already, you can get it at http://get.adobe.com/reader/.
If you're trying to open the PDFs from inside Word, then Word will try to open them. You can still open them from Word, but not by just double-clicking on the filename or selecting the file and clicking Open. Instead, you must right-click on the filename and choose Open with Adobe Reader X.
If you're trying to open the PDFs from an Explorer window (Computer) and they're trying to open in Word, then there is a problem with the file association. Right-click on any PDF file, choose Open With, then Choose Program, and select Adobe Reader, being sure to check the box for "Always use the selected program to open this kind of file."