sds to txt conversion does not make much sense for charts from Openoffice.org (.sds) since these are more of a pictures than text files. But generally speaking, any text file or text format can be exported to plain text format.
Several different sds file types exist, but none of them seem to be in format that would be obvious choice for this export, although some are in text and not binary format.
Updated: January 16, 2024