If you want to keep your documents separate, a good workflow for long documents is to do each chapter as a separate and use the Book feature to synchronize them. If you want to add pages from one document to another, you can use the Pages pallet, go to the fly-out and choose Move Pages, and when it asks you the destination, navigate to the other document. Keep in mind that if you have things like styles that have the same names but different attributes in both documents, you will likely have to choose which you want to override the other. If you want to keep them separate, rename them in the source before copying them to the destination, and they won't change.
GREAT RESPONSE !!! This worked well.