The Writer applications on the LibreOffice and OpenOffice productivity suites use the ODT, or OpenDocument Text, file format to save any documents that you create. If you received an ODT file that you want to open or edit, you can use either LibreOffice or OpenOffice for this purpose; both suites are available for download free of charge. Since Word 2013 also supports the ODT file format, you can instantly open ODT files if you already have Microsoft Office installed.
Opening ODT Files
Download and install either LibreOffice or OpenOffice (links in Resources). After installation, navigate to the location of the ODT file using File Explorer. Right-click the ODT file, point to "Open With," and then select either "LibreOffice Writer" or "OpenOffice Writer" from the list of apps. If you have Microsoft Office installed on your computer, select "Word 2013" to open the ODT file. You can also open ODT files from within the LibreOffice Writer, OpenOffice Writer or Word 2013 applications by using the "Ctrl-O" shortcut.