Single page view

By default, the viewer will calculate the initial zoom level based on the dimesion of page and the container width. So that, the document will fit best within the container.
It's also possible to set the default zoom level via the defaultScale option. In the following code, it is set as SpecialZoomLevel.PageFit so the user will see a single page in the container:
import { Viewer, SpecialZoomLevel } from '@react-pdf-viewer/core';
<Viewer fileUrl="/path/to/document.pdf" defaultScale={SpecialZoomLevel.PageFit} />;

Related example