In Drupal 8, the home page is handled by a view called "Front Page" (machine name : "frontpage").
You can see how this view displays nodes by editing it here : /admin/structure/views/view/frontpage
Basically, it displays the last 10 nodes or sticky nodes or promoted to front page nodes, using the teaser display mode. You can modify this view behavior with Views UI (URL below).
Each node can be displayed using various display modes : full content, teaser...You can create new display modes, and define wich fields you want to be printed for each, or define template files to be used for each display modes. For each field you have options (depending on field type).
So you have multiple solutions :
- edit the default teaser view mode to fulfill your needs (Content, Content Type, [your content type], Manage display, click Teaser tab and edit displayed fields)
- create a new display mode for your home page, use it in front page view
- define a new view, use it as front page view
- define a new display mode, use it in front page view and write a template file, specific for this view on this display mode, then manually print fields in it
- ...
The fastest solution would be to edit teaser display mode and add your file field in it. But it could be a good idea to keep teaser display mode intact and create your own.
More infos here : https://www.drupal.org/docs/user_guide/en/menu-home.html
Good luck with it