Powerpoint doesn't have a feature that allows importing of HTML websites or objects. Although there is a section called Objects from where you can import various formats, script or applications, there is nowhere specified that HTML is supported. Also, dragging a HTML file onto the slide will not work as it will only display it as icon without link features.
There are other alternatives if you want a flipbook effect for your slides and these are called Templates. These templates can be downloaded from all over the web because most of them are free to use.
Once a template is found, you can either double click it and it will be imported into the application or manually placed into the templates directory which can be later used from the main menu of the software.
