>>Try to look for the signature from the end of the file not beginning.
>
>For a Word 2007 file, the signature is at the same location. There is only one in the file. So, everything works for Word 2003 file. For a Word 2007 file, I guess there is a different signature that I need to use.

Yes, as I mentioned in another message, it's a regular ZIP file with extension docx/xlsx.