[Grimulkan]

The actual size of the screen is neither A4 nor A5, so there are bound to be blank spaces. In general, there is no difference between an A4 or A5 page in a digital medium like the DR, as they are both the same aspect ratio (A5 is just A4 with 50% zoom). The only thing you need to worry about is the display font size, because you can't change this (as of now) with a pdf file. So you can print something with a larger font onto an A1, and it will look the same as something with a smaller font on an A7. The paper size itself is irrelevant.

Of course, if you don't have access to changing the font size (or don't feel like doing this), you can pick any size that displays an acceptable number of lines in your specific font size. The reason your word doc looked right on an A4 is probably because it was an A4 (or letter) to begin with.

Also, Word modifies the flow of your document to account for the paper size. If you were printing a full-page image or a scalable object, the paper size would not matter.