Open Files In New Window or Tab (wp-open-files-in-new-window) free WordPress plugin

This plugin enqueues a simple jQuery script that looks for any anchor tag that has an href property to something with a file extension of 1-5 characters and makes it open in a new window or tab.

see script here

This means any link to a .pdf, .txt, .ppt, .doc, .xls, .xlst, etc will automatically have the property ‘target=”_blank”‘ added to it so it opens in a new window or browser tab.