I'm a bit confused. Are you writing about
(a) an existing 2-page A5 PDF document ;
(b) two separate existing A5 PDF documents ; or
(c) a document which you've yet to create?
If it's (a) then many printers will allow you to print as you want anyway. For example, if I open a PDF document in my PDF reader (which is SumatraPDF, but it's probably just the same with Adobe Reader or any similar software) and then go to File>Print the driver for my Canon printer offers me a 'Preferences' button. I then select 'Landscape' for printing (onto A4 paper) and 'Paper Saving'. That's all that's required.