I have to create [Rebuild an existing site] a PHP page from a CSS/HTML page. Is there any easy way for this?
Any help is welcome.

Actually, a CSS/HTML template can be used on a PHP page.

a .HTML file is treated similar as a .PHP extension only the .php has code that is executes.

What you can do is open up the original php file in notepad and take a look at where all the HTML styling is. Then just copy the html from the template index file and replace the html in the PHP file. Then all you need to do is make sure the images and css styles are in the same directory.

Since you didn't give much information, the easiest answer is this. Change all file extension from .htm to .php. php and html can be embedded in the same file and a page with only html in it can still have the .php extension, but of course it won't make any difference unless there are actually some php code in there. Also, there can (and should) still be CSS just as before. The visitors to your site won't be able to see the php code any way. For them it's still just html and CSS.

php is used to add more functionality to your site, but from the way you put it, it seems you just want to have a site build with php with nothing more than the same functionality as before. If so, then there is no need to use php.

Otherwise, you have to be way more specific on what you actually want.

Like the other guy said more info is needed.

But to say it more simple.

<?php php code here ?>
html code here
<?php php code here ?>

you get the idea. they can be mixed. any html on a php page will be treated as html