Windows Mobile 6.1 started including the files needed to open docx or xlsx files on it. You will see that this is the file types it uses when creating documents. In Word 2007 you can either save your files as doc using the drop down save as dialogue box to choose the 2000/2003 file type or you can install a patch on your windows mobile device.
The patch is located here.
Simply by downloading this file it will make your Windows Mobile device read these new file types. This is similar to the compatibility patch they have for office 2003 users.