WK3, Lotus 3 Worksheet (.wk3)
The WK3 Spreadsheet file format
The spreadsheet program Lotus 1-2-3, released by Lotus Software in 1983, used the file name extension WK3 for spreadsheets created using version 3 of the program. Those spreadsheets have been used for many data storing, organizing and sharing purposes during the prime of Lotus 1-2-3 version 3.
Technical details of WK3 files
The WK3 spreadsheets store data in the commonly known spreadsheet fashion, using a grid of rows and columns that consist of different cells where the data can be entered. WK3 files are not supported in Microsoft Excel ever since Office Suite 2007 came out.