I'm no php expert by any means, but there is an easy trick to doing that.
Take your index.html file as an example. You have a header area, body and footer. These sections are porbably exactly the same on most of your other pages too. There are probably other sections to that page that are also the same everwhere else. Like the menu bar, maybe a sidebar with static ads, that sort of thing.
Whenever you want to make a change, say to the menu bar by adding another page link, you have to then make that change in every page that has the menu bar.
Here's how to get round it.
Open your index.html file and save a backup of it as index_old.html (you never know...). Now cut the entire <head> ... </head> section and paste it into a new file. Save it as something like header.php
Note: Here I'm a little unsure of naming conventions. Every site I've seen that uses php anywhere in the page has gotten rid of the .htm or .html extension and replaced it with .php. I think it has to do with the server being able to recognise that there is php embedded in the file. Not sure though.
Anyway, at the top of the now headless index.html file, insert this line of code exactly as is:
<?php
include ('header.php');
?>
Now save your amended index.html file (minus header) as index.php - see the above note. Upload the two new .php files to the server. Now rename index.html to index_old.html on the server.
Open your browser, open your homepage and hit the refresh button on the browser. It should look exactly the same. If it doesn't then there is a problem and you simply rename index_old.html back to index.html and delete index.php. Old backout habits die hard, but they can save your bacon when things go wrong!
Assuming the test was successful, you can go through every other page and replace the <head> ... </head> section with the php code above, making backups of each file first, or course.
One annoying but essential thing you also have to do is change all the internal links to point to the new .php files, but you'll only have to do it once. A good thing to do is to take your menu bar and cut and paste it into a separate file called, for instance, menu.php. Then add the php include statement in it's place:
<?php
include ('menu.php');
?>
The new menu.php will have all the links changed to your .php files, so you only have to make this change once and copy it to all the pages.
You can repeat this idea for the "footer" section and even a sidebar, or anything else you want that is the same on lots of pages.
Then upload all the new .php files to the server. When you're happy everything works fine and all the links are correct, you can delete all the old .htm files from the server.
Whenever you need to make changes to any party of the <head> ... </head> section again (or whatever section you have replaced with the php code), you only need to do it once, then upload that .php file to the server. You won't need to change or upload any of the main data pages unless you make changes to data on individual pages, as you would have done before.
Hope that's not all double dutch!!!
