Which CLI application should I use to convert Word template (*.dot file) to the plain text?

You can use LibreOffice in the terminal.

soffice --headless --convert-to txt:Text YOUR-DOCUMENT-HERE.DOT

Check out the sources
Source1
Source2

There is also antiword (use deb-package), which extracts plain text from old (pre-XML) Word documents in a very efficient, but not always entirely correct way.