Most of the classic WordPress blog themes display full content in archive page. If you want to limit the archive post content with a read more button, then add the following snippet to your theme function.php
file.
add_filter("the_content", "break_text"); function break_text($text){ if(is_front_page() || is_archive() || is_search()) { $length = 400; // limited to 400 characters if(strlen($text)<$length+10) return $text; //don't cut if too short $break_pos = strpos($text, ' ', $length); //find next space after desired length $visible = substr($text, 0, $break_pos); $read_more = "... <br><center><a href='".get_permalink()."' class='wp-btn'>Read more..</a></center>"; return balanceTags($visible) . $read_more; } else { return $text; } }