In /etc you can find configuration file papersize which simply shows which paper size is in use system wide.

Wrong paper size (i.e. letter instead of European A4) can lead to misprinted documents, especially with the system PDF printer. In particular if you find text rows at the top and at the bottom of the paper messed up you should definitely ensure that both this config file and the PDF printer paper preferences show the same paper size.

to change paper size to A4:

sudo echo a4 > /etc/papersize

a more elegant way to do that or if you want to switch to a more exotic size:

sudo dpkg-reconfigure libpaper1

to check paper size:

cat /etc/papersize

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