I have to reduce the height of my document by 1 cm. This is easy using "Format de document..." (French for "Document Format", I suppose). I have only to reduce the document height by 28 pt. The page is trimmed by 5 mm at the top and 5 mm at the bottom. Perfect.
However, the page number (on the bottom on first pages of chapters) is now too close to the bottom of the pages. Actually, it seems sensible to move the footer upward by 7 mm and the header downward by 3 mm.
But I could not figure how to do it. I am not the author of the document, and if there is a master page, I was not able to find it.
Thanks for any help.
In fact, there is a Page menu in the Control panel and a pages panel. Thanks you both.