You can change the page of the document that is being displayed using the menu or the control in the window's toolbar.
The menu contains several commands to change the page that is displayed.
The menu is accessible from the application menu at the top of the screen and from the context menu. (Click the right mouse button on the image to bring up the context menu.)

The current page is displayed in the control's text box. The number of pages in the document is displayed in the upper right corner of the control.