I would open the pdf in illustrator, delete everything (including the numbers) but the guides. Select everything and then in the transform palette chaneg the width to 291, then hit ctrl enter to scale proportionately. Copy thsi to the clipboard.
Next make a new document in Photoshop to be 291mm x 121mm @ 120px/cm (=300dpi). Paste the illustrator clipboard elemetns into Phototshop, should fit like OJ Simpson's glove. The open your desgine psd documents and drag all your layers at once to the new docuemnt with teh die. You can then see where all the folds are to design this to match.
Finally in phothsop, you can save as a Photoshop PDF. Would be best to taek InDesign out of this job, unelss there si somehting youneed to do in Indesign.
You may need to add bleeds, and guessing the German on the bottom may mean add 3 mm bleed on each side. Mein Deutsch is nicht gut. So you may want to use canvas size to add 6mm to height and 6 mm to bottom, before transferring your lovely artwork over to the template.