The Office suite continues to improve with each new release. The 2007 version introduces a new file format, denoted by a “X” at the end (docx, xlsx, etc.), that is incompatible with previous versions.

In other words, documents saved in the Office format cannot be opened by Office 2003-compatible applications, such as the suite itself or viewers like Word Viewer. That was the case previously.

Since you will be able to open and restore files in these formats, the Microsoft Office compatibility pack will ensure that you do not get stuck with the old version.