Somewhat older .wk4 spreadsheets that were originally saved in Lotus 1-2-3 version 4 are still supported in some spreadsheet or table editors, like Excel or some open source alternatives.
With these programs it should be easy enough to export the table data from these .wk4 files to CSV or even plain text format. A text file would be unformatted however, so CSV would be more preferable for spreadsheet export.