The document was probably created in Works and saved it Works word processor format.
http://office.microsoft.com/en-us/word/hp011881161033.aspx
Install the filter, open the document in Word and resave as a Word document.
If this does not work-
If you still have Works, then open the file in Works and save it to .RTF format. This can be read in BOTH Works AND Word. Open the .RTF file in Word, save it to .doc file.
Tom