I would like to use the book cover template available in Creative Cloud, but I am unable to adjust the sizes to accomodate a 9x6 format. Is this possible in the template, or should I just set up a three-page document?
If you have modest ID skills, setting up a book cover is not a hard project. Set up a three-page doc and learn the details of creating an extended spread. It's best if you work from numbers given by a specific printer or binder, and not just generic ones. KDP in particular will give you every number you need, and I think Ingram and Lulu are just as complete.
but I am unable to adjust the sizes to accomodate a 9x6 format.
Hi @thomasb15338075 , I’m not familiar with the book cover template you are using, but to change a page size select the page in the Pages panel and use the Pages tool to adjust the page dimensions with the Transform panel. A cover setup as a 3 facing page spread (Facing Pages turned on in Document Setup) will keep the pages together as a spread when the page dimensions change:
More here, and I’ve attached the above example:
I highly recommend the 3-page method that @rob day is describing for creating a book cover. The forum thread his references provides a LOT of material. I've been teaching InDesign classes at UC Berkeley Extension since 2017, and that's the method I teach. It's by far the most flexible method.
Once learned, you can also use the technique for creating folded brochures where the panels must have different widths to compensate for paper thickness when folding.