I'm trying to self-publish a book using CreatSpace on Amazon. They want an extra 1/8" around all margins of a 6x9" book (actually more on the width) to allow for bleed. I have to generate a PDF. When I changed the page size it kept the type in the same spot, and made the pages jump back and forth a little in the PDF. It would be good if they stayed in the same place. How can I center ALL the artwork -- including the headers on the master page -- both vertically and horizontally to fill a particular page size? Thanks for any advice.
There may be a bit of miscommunication going on. You should be designing with the final trimmed page size in mind, and if you have images or solids that need to bleed, they need to extend beyond the trim size. When output to PDF, you specify whether to include crops and bleeds, and the size of the crop marks and bleed area. For example, if you want something like this crappy example I just knocked off:
You would set up your page size at 6x9 and place the images like this:
…and when output to PDF with the marks of your choice:
…you get something like this:
…which results in a PDF whose size is 6.83x9.83, but when trimmed will be 6x9. If you measure from the crop marks, the size is 6x9, and if you measure from the bleed marks, the size is 6.25x9.25, which is the trim size with 1/8" bleeds on all sides. Ask the publisher what marks they would like. They may not want bleed guides or color bars, so just give them what they want.