Info on temp files for v4.8a:

To allow multiple instances of Hex Editor loaded in up to 10 DOS windows
at the same time, temporary filenames have changed;

  Copyfile.dat  has been renamed to Copyfile.da? with ? being the process
   number from 0 to 9. This file contains the most recently copied
   hilighted area within each process.

  Hexedit1.dat and Hexedit2.dat have been renamed to Hexedit1.da? and
   Hexedit2.da? with ? being the process number from 0 to 9.

   Hexedit1.da? contains the DOS/Windows filenames in the current directory.
   Hexedit2.da? contains the DOS/Windows directories of the current drive.
    These two files are sorted with a fast heap sort.

  Markers1.dat has been renamed to Markers1.da? with ? being the replaced
   process number from 0 to 9. This file contains the markers set for
   each file number within the current process.

  Undobyte.dat has been renamed to Undobyte.da? with ? being the process
   number 0 to 9. This file contains the bytes and their location to be
   undone for each file number within the current process.

  Undofile.da? where ? is the file number loaded from 1 to 9, has been
   renamed to Undofil?.da? where the first ? is replaced with the
   process number 0 to 9. Each undo file contains each pasted area
   overwritten by the copied area to be undone for each file number
   in each process.

  Starting more than 10 processes exits with an error indicating such.

-end-
