Unfortunately, not much can open a Word 2007 document (except Word 2007) - This is not true anymore. OpenOffice can open Word 2007 documents.

Word 2007 and Word 2003 formats are not compatible with each other. Using Save As can change the formats of the Word document so other program can open the file. This can cause the loss of formatting and information when the document is saved using a different format. PDF can be used to save the document just how it looks on the screen for printing and viewing on another computer.