Web View is the mode that is selected by default. In this mode, you have access to the widget library and all the editing tools. This mode renders the report as a responsive web page as it does when shared via a link and viewed on a phone or web browser.
To view the report as it will look in PDF format (or in printed form), you can switch to Print View mode by clicking on the Print View button on the toolbar.
When you are in Print View mode, you can see the pages, headers, footers, page numbers, and other page related features. From here, you can also click on text in the cover page or in notes widgets and edit that text. You can also open the themes editor to adjust colors (as shown below). You cannot, however, open widget editors or the widget library.
The image below shows a report being viewed in Print View mode with the themes editor open.