Click a document name in the document grid to open it in the viewer.
Document controls run along the top of the viewer:
Zoom in / out and set a specific zoom level
Fit to width and Fit to height
Rotate Page and Rotate Document — rotate just the current page, or the whole document
Page up / down and go to a specific page
Toggle full-screen view
Open the annotation tools
Page thumbnails. The left panel shows a thumbnail for each page — scroll it and click a page to jump to it.
Switch documents. Expand the document list on the left to open a different document without leaving the viewer, or use the ‹ › arrows at the top-left of the viewer to move to the previous or next document.