Starting version 2.6, eForm support popup forms. Inserting it to any page is as easy as inserting a shortcode.
#1: Insert popup form to a particular page:
We shall use the shortcode to put a popup form on any page or post. Please read the guide of this tutorial to learn how.
Now when you view the page, you should see a popup button at your marked location.
#2: Insert popup form to entire site:
For this, we will insert a Widget to a sidebar which is visible across all site. Such sidebar could be Footer or Common Sidebar. It actually depends on your theme.
Please follow this guide to learn how.