Is there a way to crop all pages to the same size?

I think what you're referring to is scaling, not cropping. Cropping keeps all the pages the same size, just changes the definition of their borders. So if you make it bigger you add white space around their contents. If you make it smaller you cut off parts of them. I don't think that's what you're after. If it's scaling you want (changing the size of the pages, while keeping their contents completely in tact), then you can do it using the Preflight tool (if you have Acrobat Pro DC) or a script.

Tools> Edit pdf> Crop Pages, you can apply the crop to all pages, however the position of the copy probably varies from page to page. If you have InDesign, create a file at the desired size and use the place multi-page pdf script (Window> Utilities> Scripts> Samples> Javascripts> PlaceMultipagePDF.jsx*> Run script- from the little fly out menu). This will create an InDesign file of your book where you can easily move each page into the exact correct position (using guide lines on the left and right master pages), export to a new pdf.

*this script is included with the InDesign install, but there is a better free script called "Multipageimporter" which you can find with a google search.