Please inform us on your version of Id.
Check Layout>Layout Adjustment
I did that, but when I do this and then change my size of document to manual (i.e. the desired 347 mm by 210 mm),
the layout of photos starts moving all around the pages.
I seem to give an order to 'move' the boxes in which I've placed the photos as well. Indesign pulls them apart so to speak.
And I want them to remain in the same place as a group, just insert an extra margin of 5 cm on the sides of my pages... (where the bookpages align)
Which boxes in layout adjustment do I have to tick and which ones I don't?