WKS is a file extension for a spreadsheet file created by Microsoft Works. What is a WKS file? Spreadsheet file created by Lotus 1-2-3; stores data in a grid of cells, which may contain formulas, alphanumeric text,. WKS is the file extension assigned to spreadsheets created using Lotus 1-2-3, a spreadsheet and table creation software by Lotus. What is a WKS file? The WKS file type is primarily associated with 1-2-3 by IBM.