For optimal printing, we recommend that 8.5x11" US Letter paper be used, ideally with a 20-pound weight standard for printer paper (most common printer paper available). We chose US Letter because it's the most commonly used printer paper in the United States today. 

Although A4 paper may also provide great results for many of our targets, we did not design our PDF targets to to work with A4 paper out of the box. However, you are free and welcome to test as you wish since A4 has similar dimensions to US Letter paper.  

As A4 paper comes with slightly differing dimensions, its printout might not exactly correspond with our intended design proportions, so please be aware in case you decide to proceed with using A4 paper.