Export drawing to pdf with the same scaling

Hi,

I'm trying to create a scale 1:1 drawing of an assembly which I can take to a special store to get printed (the assembly is 30'' by 30''  and it is crucial that it is printed on one piece of paper). I created a custom size paper for the drawing and then scaled the assembly 1:1. When I export the drawing to pdf the scaling is not preserved (i.e. at 100% zoom the assembly is not the same size on the screen as it should be in reality). Is it possible to export the file to pdf with the exact same scaling? How about other file types?

Thank you,

Eyal