Hi Monika Piekarska,
Do you have all all tabs showing on Tableau Server? You might have missed this one, maybe.
If so, you should be able to export all "sheets in the workbook" (more info here: http://community.tableau.com/thread/122886)
Lénaïc RIÉDINGER, Global Community Engineer Tableau
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thank you for your reply. Finally, I've just wrote another script to merge the files.
In case thirst for knowledge Jeffrey has just published a post about PDF batch printing. Good addition to this thread