Stephen AfamO

This plugin allows you to use any HTML or PHP file as the template for any page or post.
Simply upload the file and select it. 
You can upload custom js and css files into the media library and link to them from the HTML file.
Options:
<ul>
<li>Overwrite All: You overwrite the entire theme and use your custom file</li>
<li>Overwrite Content: Keeps the header, footer, sidebar, e.t.c. Simply overwrites the body of the page or post</li>
<li>Above Content: Your custom content is simply added to the top of the page content</li>
<li>Below Content: You custom content is placed just beneath the page content.</li>
</ul>
<h4>Adding support for custom post types</h4>
By default the pulugin works with pages and posts, however, go to the settings to enable it on any other registered post type.
use the <code>hppp_post_types</code> filter to add more post types.
Like this:
<pre><code> public function post_type_modify ($post_types) {
 $post_types[] = 'custom_post_type';
 return $post_types;
 }

 add_filter( 'hppp_post_types', 'post_type_modify' );
</code></pre>

Custom HTML/PHP Post Templates

I use this on a couple sites I own and it works wonderfully.
I hope you can find it useful. 

Works like a charm

Use your HTML or PHP files for any page or post.

Platform.ly

The Platform.ly WordPress plugin provides you with a quick and easy way to add your Platformly optin forms and landing pages to your WordPress site or blog, as well as track events and more. The plugin uses the Platformly server located at <a href="https://www.platform.ly/" rel="noopener nofollow ugc">https://www.platform.ly</a>
To use the Platform.ly WordPress plugin, you must install it, activate it and enter an API key, which can be found inside the Platformly members area, in the ‘API Docs & Keys’ section.
After creating optin forms or landing pages with our WYSIWYG builders, you can add them to your WordPress site or blog in just a few clicks thanks to our plugin. Once set up, we monitor every action that your visitors take and provide you with a nice time-segmented report inside your Platformly account. The plugin supports both optin forms and landing pages created in Platform.ly, as explained below:
Pages
Pages are full-width and full-height templates that can be displayed on a particular slug or at a particular event. After you create your page inside Platform.ly, you can go and set it up to show on your site or blog. If you want to modify it later, all you have to do is edit it inside Platform.ly and save your changes. The latest version will automatically show where you embedded it, which means you don’t need to update the code.
We offer 3 types of pages:
1. Normal page – Just choose a slug name and we will show this page whenever a user visits that slug. 
2. Homepage – If you select this option, it will replace your current homepage with the one of your choice, created in Platformly. 
3. 404 page – Whenever a user visits a page that doesn’t exist on your site or blog, this page will be shown.
Optins
Optins are awesome for building up your email list.
We offer 2 types of optins:
1. Normal – With normal optin forms, you can choose a template or start with a blank canvas and create a single-page optin, with some text content and fields to ask for an email address or other contact details. You can map any field you want from Platform.ly.
2. Segmented – With segmented optin forms, you can build a multiple-pages optin. This means you can set up as many screens as you want and lead users through them as they click on different options that you set up on every screen. This is a great way to categorize your leads as they come, by adding certain tags to them, adding them to certain segments and/or using certain custom fields.
Inside the plugin, you will be able to choose how you want your optin form to be displayed. You can choose the location on the page (center, top-right, top-left, bottom-right, bottom-left), as well as the animation (pop, slide, fade) and when to show it. For example, you can show it after a certain amount of time (in seconds), after the user has scrolled to a certain percentage of the page or on exit (when the user moves his/her mouse to close the tab).
What is even cooler with Platformly optin forms is that you can adjust exactly how you want them to look on both desktop and mobile. You can build a form for desktop, make it automatically adjust for mobile and then modify the mobile version. You can have different fields to show on desktop and mobile, as well as different options. This also applies to pages, if you want to change something, you can do it from your Platformly account and the changes will immediately mirror on the site or blog where you have added the form.
Features:
<ul>
<li>Intuitive builders</li>
<li>Responsive designs</li>
<li>Auto-updates as you modify forms and pages</li>
<li>Ever growing library of templates you can choose from</li>
<li>Complete report on your forms, pages, leads…</li>
<li>Plenty of options available: choose when you want your forms or pages to show…</li>
</ul>
For more information, please visit the <a href="https://www.platform.ly/blog/" rel="noopener nofollow ugc">Platform.ly blog</a>.

Platform.ly Official

Add Platformly optin forms and landing pages to your site or blog in just a few clicks.

Custom HTML/PHP Post Templates vs Platform.ly Official