I've checked the description and functionality of this application, but WPD files are not supported. There is nowhere mentioned about WPD and WordPerfect. You will need another application for this purpose.
A simple way to convert the files is by directly printing them to PDF. You can use CutePDF Writer. Download, install and then open the WPD file and choose File > Print. Select CutePDF Writer and you will be prompted to save the file to PDF.
Download CutePDF: http://www.cutepdf.com/Products/CutePDF/writer.asp
You can also use online services for this procedure: https://goo.gl/9r0jaQ