Hi Geremia , check zoom and portrait/landscape in all places,
the software where you are working, the driver on Slackware-cups page
of that printer, and the settings on Windows, etc...
Somewhere, somebody is sending wrong settings, you must find where and who
I'm using this virtual pdf printer a few months and it is very useful,
at least you can see if from Slackware-side printing is ok.
http://slackbuilds.org/repository/14.1/office/cups-pdf/