The easiest way to achieve wp7 to doc conversion, i.e. to convert Corel WordPerfect documents version 7 (.wp7) to Microsoft Word documents (.doc, .docx), is to use Corel WordPerfect as it supports all kinds of document formats.
If you do not have access to the program, you can download a trial version that should be sufficient for a simple re-saving or a single or few documents. Otherwise, you would have to ask some of your friends with the program to convert wp7 to doc for you.