Only US/Canada use Letter page size as a default. The rest of the world pretty much uses the ISO 216 standard - i.e. mainly A4 - yet Adobe Acrobat Pro doesn't seem to provide the ability to change the page size.

Within Adobe Acrobat Pro we need both: (a) the ability set the default page size to A4; (b) the ability to easily change the size of an existing page to A4 (e.g. when creating a form).