For example, there is a .doc file in Files app and I can see what is in it. But I want to see just .doc template icon. I'm using Juno.
There is a org/gnome/desktop/thumbnailers/disable-all setting but at the moment Files does not appear to honor it. I would raise an issue at https://github.com/elementary/files/issues about this. You might point at that other filemanagers (e.g. Nemo) do have a setting do disable local thumbnails. Files only has a setting to disable remote thumbnails.
Pantheon-files uses a thumbnailer daemon called tumbler. You can disable the generation of thumbnails for PDF, Photos, Documents, etc. by editing the config file.
sudo nano /etc/xdg/tumbler/tumbler.rc
here you have to change
Disabled=true in the desired section
Ctrl+O, Enter, Ctrl+X to exit nano