Pulling in non-wordpress HTML into a WordPress Page

I am working on creating a wordpress site that will act as a sort of “diary”. Each entry of the diary is actually stored in a static HTML page that contains all of the required markup for that entry (so for example an entry for 24 January would have 24jan.html and a an entry for 3 March would have 3mar.html). These pages only contain the html necessary for the diary entry itself – i want to keep all of the header and footer in wordpress (since there are other wordpress pages in the site that are created using standard wordpress mechanisms such as posts etc). All of the styling for the pages is in the style.css of the wordpress template i’m using.

What I’m thinking is to create a wordpress page that, based on links that are clicked or via javascript, then includes the appropriate HTML into the body of the page. However, I’m not sure how to go about this. Would I just use standard php to load this dynamically within the page? If so, what plugin would I need in order to allow php within a standard page (assuming it’s not in a custom page template but in a “page” created in wordpress)? Is there a better way to go about this? I’m open to any and all suggestions.