From Just Solve the File Format Problem
EIOffice is an Office suite very similar to Microsoft Office, developed by Chinese company Evermore Software. EIO stands for Evermore Integrated Office. Office suite changed to Yozo Office (永中Office) in 2010.
All Word Processing, Spreadsheet and Presentation formats all have the extension .EIO.
Documents can be identified by the header which includes the ascii text "EVERMORE SOFTWARE INC."