Install fancybox 3.0 in wordpress without plugin

Hi, I'm trying to install the fancybox 3.0 on my wordpress page, but I can not add the data-fancybox= attribute for the images or galleries that wordpress creates from the entries.

Before, I had the easy fancybox plugin but I decided to remove it, because it loads too many scripts and the page goes slower. With this plugin I got that when I selected in the link of the image as multimedia file I recognized these as fancybox links and I opened them in the pop-up, I could also choose what types of files I wanted to open. ..

I have only added the libraries

jquery.fancybox.min.css and jquery.fancybox.min.js

I get to recognize them for the galleries that I create manually, because I can add the attribute data-fancybox="images" to the button. This is the page that works well , The images that you open are the examples of web pages below.

On the other hand, in this other , which is an entry, I can not get it done automatically, because I got it with the galleries with the code I leave afterwards, but in the single images nothing, I could add the attribute manually, but in the galleries I can not find the way.

In the fancybox 3.0 page I can not find it, I found this script in surealcms , and I have managed to open the image galleries.

Now I need you to open any image or pdf that is linked from a button <a href="... .jpg"> <a href="... .pdf"> This could be done manually, but I understand that it is most convenient to do it automatically.

$(document).ready( function() {
    // Don't execute if we're in the Live Editor
    if( !window.isCMS ) {
        // Group images by gallery using 'data-fancybox-group' attributes
        var galleryId = 1;
        $('.gallery-group').each( function() {
            $(this).find('a').attr('data-fancybox', 'group');
        });
        
    }
});

Thanks in advance