ARCHICAD 20 can back‐save project files to ARCHICAD 19 format only. When you back-save a project, an alert will warn you that elements and information that are not supported by the older version will be discarded.
When back‐saving your ARCHICAD 20 project to version 19, any library parts that were revised for 20 will be automatically replaced by their original counterparts in version 19.
If the object in ARCHICAD 20 acquired additional parameters or functions compared to the version in ARCHICAD 19, those new features will be lost when you back‐save the object to ARCHICAD 19.
When back-saving Scheme Settings to ARCHICAD 19, any new IES Fields for construction elements (2D Plan Preview, Cross Section Preview, and 3D Axonometry) will be lost.