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.
> 
> I don't know whether I am missing a trick in HTML. 
> 
> 
> 

Google thinks that in the future, there will be a feature where files can be included via an HTML tag.

> 
> 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. 
> 
> 
> 

Yes. Here's a code template in php that I made now that will work:

```
<?php 
$includepath="/path/to/your/includefiles";
chdir($includepath); 
?>
<!DOCTYPE HTML>
<html>
<head>
<title>Test</title>
</head>
<body>
<?php include "header.php"; ?>
<div>
<div style="float:right;">
<?php include "sidebar.php"; ?>
</div>
<!-- Main page content goes here -->
</div>
<?php include "footer.php"; ?>    
</body>
</html>

```

If you can copy that template and put all the php files in the same folder and set $includepath to that folder, then you'll be good. I used a div float box for a side bar but if you want to go old-fashioned, you could use a table as follows:

```
<!DOCTYPE HTML>
<html>
<head>
<title>Test</title>
</head>
<body>
<?php include "header.php"; ?>
<table>
<tr>
<td>
<!-- Main page content goes here -->
</td>
<td>
<?php include "sidebar.php"; ?>
</td>
</tr>
</table>
<?php include "footer.php"; ?>    
</body>
</html>

```

Only thing with a table is many people may frown on it because it isn't the best thing to use for responsive design.

> 
> Also I want to know whether this solution is good in SEO perspective or not.
> 
> 
> 

It will make no difference with SEO unless your server has a badly functioning disk with bad sectors attached to the requested files or the php engine is extremely slow. These things are extremely rare, but I'm sure they happen. Website speed affects SEO.