How to customize entity print pdf
It depends on which print engine you're using. I am using the following entity-print.html.twig with the dompdf engine.

&lt;html&gt;
&lt;head&gt;
    &lt;meta charset="utf-8"&gt;
    &lt;title&gt;{{ title }}&lt;/title&gt;
    {{ entity_print_css }}
&lt;/head&gt;
&lt;body&gt;
{# The footer is repeated on all pages and must be printed first. #}
&lt;footer&gt;
    {{  footer  }}
&lt;/footer&gt;
{%  if cover_page  %}
&lt;div class="cover-page"&gt;
    {{ cover_page }}
&lt;/div&gt;
{%  endif  %}
{# The header is repeated after the cover page for all pages. #}
&lt;header&gt;
    {{  header  }}
&lt;/header&gt;
&lt;div class="page"&gt;
    {{ content }}
&lt;/div&gt;
&lt;/body&gt;
&lt;/html&gt;


The header and footer must be styled with position: fixed, after which they are displayed on every page.

I haven't found any great combined reference for the entity print module, but searching for what you want to accomplish along with your print engine's name should be helpful.