You can format a document for printing on ISO 216 A4 paper size with
@afourpaper command. Write the command on a line by
itself near the beginning of the Texinfo file, before the title page.
You may or may not prefer the formatting that results from the command
@afourlatex. There’s also
@afourwide for A4 paper in
@afivepaper for A5 paper, and
See Format with
and Preparing for TeX, for other ways to format for different
paper sizes that do not require changing the source file.