It doesn't seem possible to convert STD OpenDocument drawing templates to plain text files, as these *.std files contains graphics, not texts.
Found 2 different conversion types using the same filename extensions.
Conversion std to txt type 1:
Convert from OpenOffice.org drawing template file to Simple text file.
Microsoft Windows software - convert std to txt on Windows
Older multi-platform office productivity suite
File type (from-> to)
Convert from std file format
OpenOffice.org drawing template file
Simple text file
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned std to txt. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert std to txt on OS X
A full-featured set of office applications for Mac OS X
Conversion std to txt type 2:
Convert from OpenOffice.org drawing template file to T602 document file.
Multiplatform software - convert std to txt on any platform
A free multi-platform productivity office suite for Windows, Mac and Linux