Take a pdf, where one side of a card is on each page. Front side and back side alternating: page 1
----------
- card 1 -
- front -
----------
page 2
----------
- card 1 -
- back -
----------
page 3
----------
- card 2 -
- front -
----------
page 4
----------
- card 2 -
- back -
----------
etc...
Then, put them into a new pdf with DIN A4 pages, where the cards are located that if printed double-sided the front and the back of each card is exact back-to-back. So if cut out, you have double-sided cards again. There are eight cards on each page, four in a row with two rows.
page 1
---------- ----------
- card 1 - - card 2 -
- front - - front -
---------- ----------
page 2
---------- ----------
- card 2 - - card 1 -
- back - - back -
---------- ----------
There are pdf files containing play card of Black Eye (Das Schwarze Auge - DSA) with gear and spells, etc. On each page of the pdf there is one side of a card, front side and back side alternating. This script is used to be able to print them to DIN A4, cut them out and for example to shrink-wrap them.