Document
What is a .bak file?
A .bak file is a backup copy made automatically by a program before it changed or saved something. It's the same content as the original file, just parked under a different name.
Work on a copy. Renaming the only backup you have and getting it wrong is a bad afternoon.
This extension has been used by more than one format
4 different formats have claimed .bak over the years, so two files with the same extension aren't necessarily the same kind of thing.
How to open a .bak file
- WindowsThe program that made it, after renaming .bak back to the original extension
- MacSame trick — rename and open with the original app
How to convert a .bak file
- The standard move: copy the file, then rename mydoc.bak to mydoc.docx (or .psd, .sql, .dwg — whatever the original was).
- Not sure what it was? The filename usually keeps the original name in front of .bak.
The technical record
For archivists, developers and the merely curious: these are the PRONOM registry entries for .bak.
| Format name | Version | MIME type | PUID |
|---|---|---|---|
| Back Up File | — | — | fmt/941 |
| Calc602 Spreadsheet file | 1.51 | — | fmt/1697 |
| Calc602 Spreadsheet file | 1.00 | — | fmt/1698 |
| Calc602 Spreadsheet File | — | — | fmt/1773 |