Microsoft Office 2007 has new extensions - the .doc Word documents are now .docx while PowerPoint and Excel also have new file formats, .pptx and .xlsx respectively.
What’s also great is that these new files are much smaller. In Word, for example, you’ll notice that these files are almost HALF the size of the .doc files. They are compressed, so the file sizes are much smaller, making for friendlier email attachments. They are also less vulnerable to corruption: If you’ve ever had a case where you couldn’t open a document that didn’t survive the email process, these new file formats are much better at recovery; damaged files can still be opened, and the data can still be saved.
These new file formats are called the Open XML Formats. They are open file formats that any program can use, and make it much easier for other programs can read and write them the same way Microsoft Office does. This makes it easier to exchange documents with other people, and helps other programs and users know that whatever is in your Microsoft Office files can be shared more easily with other programs.