Question: I don't know whether I am missing a trick in HTML. I have one simple HTML website which has over 100 HTML pages. For each page the header, sidebar & footer section are the same but the content is different. Can I simply make this site like Wordpress where the page is formed by header.php, footer.php, page.php & sidebar.php. I know I will still have to work on page.php kind of files. 

This will simplify the file structure of the site. Also I want to know whether this solution is good in SEO perspective or not.

Answer: 
Content Management Systems such as WordPress don't really improve SEO since you can do everything in Static HTML form than you can in a WordPress. 

WordPress just makes thing's a hell of lot easier for managing your pages as well as creating SEO friendly URLS. You should see using a Content Management System as making your job easier and freeing up time to make even more content - If we was to save time saved and time spent on constructing pages then yes it does improve SEO.
Yes, you can do this by using PHP `include` statement to call your header, sidebar and footer whenever you need to include them in a page using `<?php include 'header.php';?>`

> 
> **Note:** In this case would be better to create files with the **.phtml** extension, so you can either put HTML or PHP code inside of it. `<?php include'header.phtml';?>`
> 
> 
> 

* The include (or require) statement takes all the text/code/markup
that exists in a specified file and copies it into the file that
uses the include statement. Including files is very useful when you want to include the same PHP,
HTML, or text on multiple pages of a website.
* Including files saves a lot of work. This means that you can create a
standard header, footer, or menu file for all your web pages. Then,
when the header needs to be updated, you can only update the
**header.php** file.

Let's say we have a code for the header within a file called "**header.php**" that looks like this:

```
<header class="header">Welcome to my website!</header>

```

To include the header file in a page, use the include statement:

```
<html>
<body>

<?php include 'header.php';?>
<p>Some text.</p>
<p>Some more text.</p>
<footer class="footer"> ... </footer>

</body>
</html>

```

When to use include and when to use require?
--------------------------------------------

The require statement is also used to include a file into the HTML/PHP code.

However, there is one big difference between include and require. When a file is included with the include statement and PHP cannot find it, the script will continue to execute, while when using the require statement a fatal error will be produced:

* require will produce a fatal error (E\_COMPILE\_ERROR) and stop the the script  

`Use require when the file is required by the application.`
* include will only produce a warning (E\_WARNING) and the script
will continue  

`Use include when the file is not required and application should continue when file is not found.`