u/Squeaky_boots224

I am currently in the process of getting my first book printed, and when I received the eproof I noticed the interior pages were cropped too much. I rejected the eproof, explaining the problem, and they got back to me saying that the pdf file I sent is 9 x 13 inches, and it needs to be 5.25 x 8 inches. I've tried fixing it in Adobe Acrobat, but the instructions on how to change the size/format of a document are outdated, and I've tried pretty much everything I can think of on Pages and on the pdf and nothing seems to successfully change the format. Does anyone know how to change this? I use Pages for writing but I am willing to try other platforms.