Need Help opening converted file in Pages

I have a Mac and use Pages as my word processor.  Pages converts Word documents into its format so that they can be opened, read and edited.  I have never been unable to open/use a document opened this way . . . till now. The downloaded document won't open in Pages.  It says it is an "invalid format."  I hope someone can help me.  The purchase of the Adobe program is no value to me if I can't use it, and I need to be able to use documents in this way.  Thanks in advance.