Start your code this way if you want to compile your text with either pdflatex or latex. Match your needs.
\RequirePackage{ifpdf} \ifpdf \documentclass[pdftex,letterpaper,12pt]{article} \usepackage{lmodern} % \usepackage{textcomp} \else \documentclass[dvips,letterpaper,12pt]{article} % \usepackage[active]{srcltx} % for dvi viewers supporting source code mapping \fi
But you can set the default zoom size in the settings of your viewing options. Evince viewer allows you to customize the top bar buttons, add zoom buttons.
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