How to open pdf in a popup in php

Basically I am using BSK PDF Manager Plugin in WordPress and want to open the the pdfs in a popup when someone click them.

 
 /* This is the href code of the plugin and what I tried to open 
 
$pdf_title_str = '<a href="'.esc_url($file_url).'"'.esc_attr($open_target_str.$nofollow_tag_str).'  title="'.esc_attr($pdf_item_obj_title).'" class="bsk-pdfm-pdf-link-for-title pdf-id-'.esc_attr($pdf_item_obj->id).'">'.$pdf_title_str.'</a>';