Dreamweaver now has Bootstrap 3.4.1 and 4.3.1 versions integrated in 19.1 release. 

By default, a new site is created using Bootstrap version 4.3.1. After you create the document, you find the css, and js folders in the site root folder. However, if you want to create the site using Bootstrap version 3.4.1, you can use manage sites and settings. For Bootstrap version 3.4.1, you can see the css, js, and fonts folder in the site root folder.

For more information, see Design responsive websites using Bootstrap.