.FM3 File Extension
File TypeLotus 1-2-3 Spreadsheet Format File
What is an FM3 file?
File created by older versions of the Lotus 1-2-3 spreadsheet software; contains the display formatting for a .WK3 worksheet; can include formatting data for cells, borders, fonts, shading, and other display elements; can be opened by some older versions of Microsoft Excel.
Even though Lotus 1-2-3 separated out the formatting information for some spreadsheet files, recent spreadsheet applications do not use this convention.