Make page dimensions from Page Tool and Page Setup match
I'll often have to change the size of page using the Page Tool. The problem is that if anyone opens the Document Setup dialogue box, it only shows what the original dimensions of the page are – not the actual dimensions.
When there are multiple pages in a document with various sizes, the Document Setup dialogue window should notify that that's the case.

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Morten commented
This is important! Just got a document from another person, with one page, where I checked the Document Setup and generated the PDF - which was another size.
Would be tedious/impossible to have to check every document and every page with Page Tool. -
Anonymous commented
A simple warning triangle would do the trick, similar to when a link is modified but not updated, a visual indication that the size you see in Document set up may not be the actual size of the pages...