SELECT COUNT(xf_attachment.attachment_id)
FROM xf_attachment
INNER JOIN xf_attachment_data ON xf_attachment.data_id = xf_attachment_data.data_id
INNER JOIN xf_post ON xf_post.post_id = xf_attachment.content_id AND xf_attachment.content_type = 'post'
INNER JOIN xf_thread ON xf_post.thread_id = xf_thread.thread_id
WHERE xf_thread.node_id IN(70) AND LOWER(xf_attachment_data.filename) LIKE '%.pdf';