A number of situations came up recently where we needed to copy maps from one project to another. We do this at OpenPoint when we're helping you with changes to the format / styling of your system maps. We've found it's also useful for our utility clients to know how to do this as well. A great example -- let's say you want to make a change to the color of a point or linear symbol. This is something you can easily do yourself so you may want to go ahead and make that change. If you have multiple computers in the office that need this change, it wouldn't be too difficult to go to each computer, open the map project and make the changes. However, if you had a number of changes, this would be more time consuming and you might accidentally miss a step.
One solution is to export you map changes to a file with a .MAPX extension. You can then import this map into the map projects used by anyone else at your utility.
This video demonstrates how to copy a map project from one project to another using ArcGIS Pro.