Documents are displayed with a border outside the page. This free space eases editing of layers lying partly or completely outside a page. This border can be adjusted separately for document and picture mode (see chapter 2.11). Furthermore you can setup, whether the size of a document window is adjusted after zooming in or out.
Deactivating 3-D Document Frame draws the page border as simple line.
PhotoLine is able to show the printable area in documents. Color of Print Frame controls the color used for drawing the printable area.
After opening an image or document it will be zoomed to show its complete content. Documents are always zoomed freely. By activating Fix Zoom Images When Opening images additionally allow to the restrict the zoom factor to even fraction like 50%, 25% and so on.
On macOS with a screen with Retina resolution there is also the setting Use Retina Resolution. If you turn this off, the screen output will be in a slightly reduced resolution. If you are doing image processing, the differences to full resolution are hardly noticeable, but the screen output is much faster.