Google Slides – Embed iFrame in Presentation

According to the Gmail blog, an iFrame is used to host the code which handles gmail so that messages opened in new windows can be used without having to reload resources, and can persist even if the parent window is closed. See this blog post for some more details on how it works.

For the technically curious among you, our friends on the Chrome team made it possible to transfer the code that runs Gmail from one window to another as the window closes. When the window that hosts the code fires an unload event, we move the iframe with the code to a surviving window. Everything continues to run, including timers and outstanding requests.

Unfortunately page numbers in Presentations hasn't been implemented yet.

We don't currently support master slide functionality, so you'll need to insert numbers and logos manually.

Source

Its likely that i will be in the future - but no idea when.

Someone on another forum suggested a workaround by using the features built into Adobe Acrobat to add the page numbers (Open the document in acrobat, open the tools menu, goto Pages > Header and Footer > Add Footer/Header)