These instructions will show you how to make a ".ps" file (also known as a "postscript file"). Simply put, you will print to a file, rather than to paper. Normally, when you click Print, your file is sent to the printer, the printer receives it, and puts it onto a piece of paper. Making a postscript file is the same procedure, except the data is sent to a file rather than a printer and paper. Keystone Book Printing can make a PDF from this file.
This method is for InDesign CS4 for PC and for those who do not own the full program of Acrobat. The steps and illustrations are based on Windows 7. If you have a different operating system, the steps may vary slightly. If you own Acrobat, go here.
With your text or cover file open in InDesign, go to File > Print.
In the General Tab, use these options for the areas in blue below:

In the Setup Tab, (Setup on the left side, not the bottom button) set your paper size to Custom. For text files, the width should match your final trim size width, and the height, your final trim size height. Cover files should be set to fit on Width: 13 in. and Height: 19 in. Make sure your Page Position is Centered.
