This adds a rectangle around each logical page:
\usepackage{pgfpages} \pgfpagesuselayout{4 on 1}[a4paper, landscape, border shrink=5mm] \pgfpageslogicalpageoptions{1}{border code=\pgfusepath{stroke}} \pgfpageslogicalpageoptions{2}{border code=\pgfusepath{stroke}} \pgfpageslogicalpageoptions{3}{border code=\pgfusepath{stroke}} \pgfpageslogicalpageoptions{4}{border code=\pgfusepath{stroke}}
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