Directory / plugin
WP URL Extension
v0.2 · by EviLex
Adds .html, .php, .whatever to pages, post, custom post type with rewrite rule
About this plugin
Adds .html, .php, .whatever extension to url of all pages, post, tags, custom post.
This Plugin related with rewrite rules so if anything problem seems in loading page with .html, refresh the permalink once
Go to Settings->Permalink and update it.