pages rounded corners
There is no way to predict how a project with rounded corners will look, be it a book, business card, flyer... We can create boxes with rounded corners, but we don't have the option to do the same with pages, choose the type, radius...

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Jan Krause commented
Rounded corners are not produced directly by the paper machine; they are created through die-cutting. Likewise, InDesign cannot simulate the presence of die-cut windows on the page.
Such elements should be defined using a die-cutting form represented with a dedicated spot color. Rounded corners may be constructed within the layout and assigned the preview-background-color, allowing them to be hidden in the preview for visualization purposes.