1 PHP Page formated from 3 separate html files

I have 3 html pages: 1. A header with a navigation menu 2. Center content 3. Bottom contact I need these 3 pages merged into 1 page keeping the header and bottom static on the site. This needs to be coded using PHP. The top navigation file will need a little formatting. The purpose of doing this is so we can simply make changes to 1 file when we need the navigation menu changed instead of each page on the site. When someone clicks on the top navigation or bottom contact the corresponding page will show up in the center area. I need this done quickly.