To see if it is a printer problem here are two sample files, a dxf and a pdf made from it.
The settings in the dxf are for letter format and 1:1 scale. When the printing procedure asks to change the settings ignore it. It only concerns the printing margins, not the scale. Truly it is a nuisance and should be worked over. On Windows you might get a printing offset, which you can compensate by shifting in Print Preview.
If the pdf gets printed wrongly scaled too, it means it is not LibreCAD's fault.