ArcMap can save an MXD file that can be opened with a previous version of ArcMap.
Instructions provided describe how to save MXD files in a format compatible with earlier versions of ArcGIS.
- Click File > Save A Copy.
- In the Save as type drop-down menu, select the compatible ArcMap version, for example ArcMap 10.6 Document (*.mxd).
- Browse to an appropriate file location and type a filename.
- Click Save.