Hello @Tom Wilson
WHMCS does not currently support removing the .php extension from files. We have however introduced friendly URLs to more and more areas of the product.
As outlined by my colleague John on our Feature Request Board
We introduced a new Friendly URLs feature which brings the potential for more human-readable URLs to different parts of the system. You can see an example of this in the MarketConnect landing pages, eg: /store/email-services.
Unfortunately I cannot provide an ETA on this and any announcements such as this will be made on our Blog or in the WHMCS Changelogs