How can I remove PDF download button?

I am using the pdf_reader module and showing my PDF on the node. Now, I am supposed to hide the download button. For this purpose, I wrote the below javascript file:

jQuery(document).ready(function($) {
  document.querySelector('#download').style.display = 'none';
});

It's also in my theme's libraries.yml file. The last thing I did was write a hook_preprocess_node implementation and put in the below code:

  $node = \Drupal::routeMatch()->getParameter('node');
  if ($node->getType() == 'e_dergi') {
    $variables['#attached']['library'][] = 'conference_lite/custom';
  }

But I can't hide the download button for the life of me. What else should I try?

If your theme name is fluffiness in "fluffiness.info.yml" add following lines

libraries:
  - fluffiness/global-scripts

in your file "fluffiness.libraries.yml" add following lines

global-scripts:
  version: 1.x
js: 
  js/fluffiness.js: {} 

dependencies:
  - core/jquery
  - core/drupal

in your file "js/fluffiness.js" add following code

(function (Drupal, drupalSettings, once) {
   Drupal.behaviors.hideElement = {
     attach: function (context, settings) {
      jQuery("#download").hide();
     }
   }
 } (Drupal, drupalSettings, once));