you would need to convert the HTML pages to php pages by changing the file extension from .htm to .php
the only diferance between a php page and an html page is the extension.
by using the php extension it tells the server to process the page through the php processor, and run any php code on the page before sending the HTML to the browser.
HTML and php code can be used on the same page.
we have a video tutorial for using Power CMS to create a blog:
that tutorial also explains creating editable regions.