Orientation et dimension

@sylvainc56416734 yes and no. Acrobat's 'Organize Pages' tool can rotate pages and 'Define Page Zone' can attempt to resize, it seems to have limitations, especially when dealing with pages that were originally in a different orientation. Based on your experience and the observed behavior in Illustrator, it appears Acrobat isn't consistently reinterpreting the underlying page dimensions or orientation for content that originated as landscape. For reliable and consistent results in unifying page size and orientation across a mixed PDF, it's often more effective to address this at the source of the PDF creation, or use more specialized pre-press tools designed for consistent page imposition.

Essentially, when you use "Organize Pages" to rotate a landscape page to portrait, Acrobat often adds a rotation instruction to the page's metadata. The viewer (Acrobat itself) reads this instruction and displays the page rotated. However, the underlying content stream of the PDF itself might still be in its original landscape orientation. When you use "Define Page Zone" (which is essentially modifying the Crop Box), you're defining the visible area of the page. You're not actually scaling or rotating the content within that area. If the content stream is still landscape, cropping it to a portrait size will just cut off parts of the content, or make it appear squashed if it's then forced into a different aspect ratio during display. What does that really mean? Illustrator reads the raw content stream of the PDF. If Acrobat has only applied metadata rotations or crop box changes without truly re-rendering the content, Illustrator will ignore those metadata instructions and display the PDF as its content stream dictates – which in your case, is still landscape!

You could, but I am worried it might flattens the transparencies, you could try printing the modified PDF back to a new PDF. Set the paper size to 214 x 301 mm (Portrait) if this is the desired custom size. When you "print to Adobe PDF," Acrobat essentially re-renders each page of your document — it is a slight work-around it just means more work for you