If you know the Mac OS application which can work as ODT file opener you can choose the "Choose Application." option in the error box to associate the file extension and open ODT file in it.If a ODT file is not opened in a Mac OS application and you instead get a "There is no application set to open the file" error message you can click on "Search App Store" in the error dialog and Mac OS will show you applications compatible with ODT file.Find a ODT file in question in Mac OS Finder and double click on it to launch the corresponding application.
Please note that Open Document Format used in ODT files is different from "Office Open XML" which is used by Microsoft Office (. These include: NeoOffice, Corel WordPerfect, Lotus Symphony, Google Docs online service. You can open ODT files by several programs other than Open Office. Open Document Format is XML based and therefore easily portable. These files contain word processing documents. ODT file extension is used by Open Document Text files that are created by the OpenOffice software suite.