New to illustrator 1

[kushii]

I am new to adobe illustrator, i am designing a A5 double sided leaflet.My Question is to design a double-sided leaflet do i have to design two pages(files) or if i can design on both sides of the page(artboard).

 

[apepp]

...turn on trim marks and include bleed values in the file > save as > PDF dialog as well, after selecting the preset "PDFx-1a:2001"...

andrew