Use SAVE AS

When a Word Perfect (wpd) file is opened in Word it will convert the page breaks to section breaks, among other little formatting changes.

You can save your file in WP for yourself, but before you transfer it to your client you should use SAVE AS to convert the formatting. Look for File Types of "MS Word (.doc)"

I suggest trying whatever File Types are available in your WP program for converting to MS Word and see which one works best for them. Using the most recent version makes sense, but it is not always the case.