You can import waypoints, tracks and routes from a standard GPX file. Not all the possible attributes within the GPX file are supported, so keep the original if the contents might be important.
Importing GPX Files: Some sources of GPX files create waypoints for every point on a route which can make a mess of an existing itinerary resulting in a laborious cleanup operation. If you do not fully know the contents of a GPX file you wish to import, create a new itinerary for temporary purposes and import the file into the temporary itinerary. Check the contents and delete any elements from the itinerary that are not required. You can then use the copy-and-paste functionality to copy the desired contents to the ultimately intended itinerary.