Using simple cell to cell "=" links into an unopened workbook  was a
method for recovering data  from a damaged and un-openable workbook (
actually I think it was before workbooks - just a sheet).

Short - Create a Link:
Type "=" then another cell. A formula automatically results. The
other cell can be in another workbook/file.

long - easy to do, many words to describe)
The original algorithm that I saw first instructed you to create (in
a destination sheet/cell) a link to an open, blank, "surrogate" sheet
(by clicking an "=" then clicking in the surrogate's source cell).
Then you changed the workbook name in the destination cell's resulting
formula to the name of the damaged workbook. Then copied that formula
over the expected data area. Whatever data 'came' was recoverable.