WK4 is spreadsheet file created by Lotus 1-2-3, a document editor included in Lotus SmartSuite package.

WK4 is a standard spreadsheet file that stores data in cells organized into rows and columns. Each cell can contain arbitrarily long strings of characters, numbers, or formulas (a formula is a function that returns a value based on input data). WK4 files were also supported by older version of Microsoft Excel. Lotus 1-2-3 was developed in 1982 and is no longer used.