Can we hide option download so users can read only?

Yes, you can do that by creating a specific theme and hiding the download button in the CSS.

Once you have generated your new theme (or chosen the theme you want to edit), you have to modify the books.css and comics.css files by hiding the #details_download id.

#details_download {
    visibility: hidden;
}

I did it for the default theme, you can download the modified version here.

THANK YOU