If you enable the ‘Tidy Links’ setting in your Rapidweaver preferences it will do that but only for files that are named either index.php or index.html, it won’t work for contact-us.php
In those instances, you’d want to name the folder contact-us and the file index.php (or index.html)
Oh, and to get to that, go to the page sidebar and General Settings, then click the little ‘Advanced’ button in the bottom right of that window
While it probably isn’t required to keep it working, you may also want to delete the old files from the web server. RW doesn’t delete files when publishing so it is up to you to clean up the old stuff. I’ve run into problems when adding a stack to a page that switches it from html to php and then it is ambiguous as to which file should load when both index.html and index.php are in the directory.