In addition to Fergus,
a Doc file is a free style text file
a XLS file is a style descibtion
and when you did mean
a XML file that is a structured data file.
and to make it complete
a HTML file is a free style text file for with the posibitlity to use
the two above (and more things).
As Fergus and Cor have intimated, this can't be done. At
least, not directly. Can you describe more exactly what it
is you need to do? Do you have documents in Word with
tables, for example, that should go into Excel? Or...?