Are you using A4 stock folded to create an A5 card? Side fold? It this is the
scenario, use the booklet setup.
If you are using A5 stock folded to create an A6 card you will have to setup a
custom size in your printer for A5. The page setup will still be a booklet.
If you are trying to create top fold card, you need to insert two pages. Page
three will be your message page. Refer to print preview. Any object or text you
place on page four will have to be manually rotated.
It would be helpful to know the version of Publisher you are using.
