You can zoom all pages of a PDF for all users using the zoom tool. Zooming is saved to the PDF file, so it affects all pages of that PDF and all users who are viewing that PDF.
Pinch to zoom
Place two fingers on the screen and "pinch" them apart to zoom in, or together to zoom out. Once you are satisfied, tap End Zooming at the top right.
Zooming a PDF changes the zoom for anyone else viewing the same file on a device that has the same screen aspect ratio. iPads and Android devices with a different aspect ratio won't see your changes.