You would be adding a template page to a pre-coded theme on your website. The answer is yes, you can add template files that only affect specific sections of your site and have no impact on the pages/posts already on your site.
You probably want to become familiar with the information in this link before beginning.
https://developer.ww.wp.xz.cn/themes/basics/template-hierarchy/
Also, make a complete backup of your site before you begin any work in case you need to roll back to the original condition. You honestly never know how much what you do will impact other areas and it is best to be safe than sorry.
Usually you would make a copy of the file index.php in your theme’s folder then change it’s name and make your mods.
are you talking about ‘template file’ as in https://developer.ww.wp.xz.cn/themes/template-files-section/page-template-files/ ?
in this case, you could use FTP to upload the template file into your theme’s folder.
or do you mean ‘theme’ ?
Hi @alchymyth
I meant theme. If there is a wordpress theme I like and would want to use it to add additional pages to my current website. Is that possible?
no. You can only use one theme for your wordpress site. To add pages just click on add new. If you want pages in your WordPress to look different than other pages you will have to create a new page template and new CSS to style it and select that template in your page options.
Tip: Call a web designer!
@jaycbrf, thanks for the info on the theme.