It doesn’t work for any URL in the world, just WP.com-hosted ones. But to be frank, who likes long stressful stuff these days? This is because an unknown percentage of your recipients read emails with a program that doesn't execute JavaScript or store cookies. With a list that sorts each PDF in order of performance.
Anyone using the link will need to know the password to proceed to its final destination. Enabling Ad-hoc link tracking Configure your Adobe Analytics framework to enable ad-hoc link tracking.
When this feature is used, links to your site that Sailthru includes in your email campaigns are wrapped in a redirect URL beginning with link.