What is the primary use of the INDD file format?

INDD file format is used to store everything needed for complex publications: text, images, formatting, styles, and more.

INDD files are the native file format of Adobe InDesign, a program used for professional page layout design. Designers use INDD files to create magazines, newspapers, brochures, books, ebooks, and any other visually rich layouts intended for print or digital viewing.