how do i change a larger file into a smaller one?

Hi, @Edward379358146yam, first off congrats on writing your book. I did that a number of years ago and it's a very satisfying accomplishment.

Look, the BEST way to do what you need to do is to go back to Word, go into the Format menu, select Document, and set the Margins as follows to have the text be within 6 x 9. This may be what they want.

However, that means that the text will be at 6 x 9. If there is a gutter of blank (empty space) around the text, find out how much the publisher wants/needs. Also, if the book has page numbers (probably) and there are many other parts of a book that I do not know if you're responsible for or if the publisher is responsible for. In my case, I was handing the publisher a camera-ready copy of my book.

What I'm saying here is that the easiest way to achieve their goal is to set it up in Word and generate the PDF from there. Trying to set this up in the PDF is more trouble than it's worth. You need to contact your publisher and ask them how to set up the desired margins in Word so that they get exactly what they want. Chances are they've done this before and know what to tell you. They very probably have a write-up all set up to send to you.

For more details about what "can" be in a book, see https://scribemedia.com/parts-of-book/

Good luck