Will Popup Maker Work on WordPress.com Hosted Sites?

Yes.  The Popup Maker plugin available from the WordPress.org plugin repository can be installed on any WordPress.com hosted site operating on the 'Business' subscription plan.  The plugin can be installed from the WordPress.org plugin repository via the site admin page.  See WordPress.com's product pricing for details.  

Important! Popup Maker plugin extensions cannot be installed on WordPress.com because their hosting does not allow plugin uploading from an external source. For example, a Popup Maker plugin extension downloaded to your computer could not be uploaded to a WordPress.com hosted site. 

If you intend to use a Popup Maker plugin extension on your site, select a web host other than WordPress.com for your hosting needs. There are many fine independent companies that specialize in hosting WordPress sites.