Once you open the file, you will have to save it as a new file, and then choose a new text format that supports RICH Formatting. You can convert to a DOC file or OpenDocument Text format and so on.

To export InDesign document (INDD) in Word, you can convert InDesign file to PDF and then to Word, or export InDesign file as Rich text Format.

Ted Landau laments the lack of full support for Rich Text Format (RTF) files on his iPad.