An Odt file is a text document created by OpenOffice and LibreOffice.
Odt files are similar to Word .docx files.
Check file format:
$ file doc.odt
doc.odt: OpenDocument Text
An Odt file is a Zip archive containing xml files.
Let unzip it, and read content.xml file.
unzip doc.odt
cat content.xml
Or use odt2txt to extract text:
odt2txt doc.odt