.WPD is the file format used by WordPerfect word processing program. FileInfo list of file extensions Rarely, WPD is used as an extension for other programs’ word processing documents.
WordPerfect was the dominant word processor software in the 1980s and early 1990s, but lost the market battle to Microsoft Word eventually. WordPerfect was purchased by Corel Corp. in 1996.
In general, you need to open the files in the program that created them, or convert them to a format that is usable by other programs. If you have access to WordPerfect, open the file, and then save it as RTF (Rich Text Format), which Word can open.
Microsoft Word can open WordPerfect word processing files of version 6 and earlier
http://office.microsoft.com/en-us/word/HP052742911033.aspx
http://www.columbia.edu/~em36/wpdos/wptoword.html
ABC Amber Standalone WordPerfect converter (Commercial – 30 day free trial) http://www.thebeatlesforever.com/processtext/abcwordperfect.html
NeoOffice for Mac can open WPD files http://www.neooffice.org/neojava/en/index.php
as will OpenOffice (Win, Mac, Linux) http://www.openoffice.org/product/
You can download a trial version of WordPerfect Office from Corel here
http://www.corel.com/servlet/Satellite/us/en/Content/1152796555406
List of converters to HTML from many different file types http://www.w3.org/Tools/Word_proc_filters.html