Usually, its not possible to include PHP files into HTML pages. Here i got a way for this which works. Its nothing but using .HTACCESS.

Create a .HTACCESS file in the root folder or a specified folder.
Add the below code  into your .HTACCESS file

Options +FollowSymLinks
AddType application/x-httpd-php .htm

Thats it

Now, you can include PHP files into your Static HTML Pages.