Problem with printing double sided

[Lore5C92]

Hi! I'm new at using Illustrator and Adobe CC in general. I made a sort of folder that must be printed on both sides. One side is the first artboard and the backside is the second artboard. The folder is 240mm x 60mm. I want to print it double sided and with two samples on every paper. But I can't make it work in Illustrator or in PDF. Can someone help me out? 

Thanks!

[Larry G. Schneider · Accepted solution]

Try it with a piece of paper. The key is that the two bottoms must be opposed.