Opening Scenario: You’ve just received a beautiful Adobe InDesign package from a freelance designer. You double-click the .indd file, and your screen freezes. A cold, gray error message appears: “This file was created in a newer version of Adobe InDesign and cannot be opened.”
The primary way to "downsave" a file is through the export function within InDesign itself. how to convert indesign file to older version
How to downsave an InDesign file to open it in an older version The Ultimate Guide: How to Convert an InDesign
If you are sending a file to another designer using an older version, the Package command is often safer as it includes all necessary assets. Go to File > Package. Export IDML and open in target version
Method 1: The IDML Workflow (The Gold Standard)