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.
Example:
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;
}
}