Proper way to switch paper size?

Question

Related question: Changing a4paper to letterpaper

I used to type all my LaTeX in letter size. Example:

\documentclass{article}

\begin{document}    asdf    \end{document}

However, we switched printers, and now I need everything to be A4 size. I tried

\documentclass[a4paper]{article}

\begin{document}    asdf    \end{document}

However, it still resulted in letter-sized articles.

So I asked a colleague how he did his size change. His response was astonishing:

\documentclass{article}
\usepackage{typearea}

\begin{document}    asdf    \end{document}

Even though he did not specify the A4 paper size anywhere, this command already changed the paper size to A4. On the other hand,

\documentclass[letterpaper]{article}
\usepackage{typearea}

\begin{document}    asdf    \end{document}

allows him to quickly change back to letter.

My question is: what is the "normal" way of modifying the paper size of an article? Surely, it cannot be by including this obscure package in the headers, and never referring to it again.

p.s., I'm compiling this PDF on an embedded device, and therefore including the package {geometry} makes my PDF compile more slowly; I'd prefer a solution without it, if there's a simple one.

Answer 1

You need code to set the pdf paper size. article is too old, and so doesn't it on its own. The needed code depends on the engine/backend. E.g. for pdflatex this would work:

\documentclass[a4paper]{article}
\pdfpagewidth=\paperwidth
\pdfpageheight=\paperheight
\begin{document}
abc

\end{document}

This is a bit cumbersome so a number of packages do this for you. typearea is one of them but will (probably) change also other layout values. graphicx is another one which I normally would use:

\documentclass[a4paper]{article}
\usepackage{graphicx}
\begin{document}
abc

\end{document}