What is the WBK file format?
.wbk (Word Document Backup) files store backup copies of Microsoft Word document files. A .wbk copy can be used to recover a modified, corrupted, or deleted document. These files are automatically generated when users enable the "Always create backup copy" option in Word, which is turned off by default. Each time a document is saved, Word replaces the previous .wbk with a fresh copy of the document as it looked before that save - the file is typically named Backup of <document>.wbk.
Microsoft Word also uses .asd files for saving timed crash-recovery snapshots, but .wbk and .asd serve distinct purposes. A .wbk is the deliberate previous-version backup created on every manual save when the backup option is enabled, whereas an .asd is an automatic, time-interval snapshot used for crash recovery.
Internally, a classic .wbk file is structurally identical to a .doc - it uses the OLE2 Compound File Binary (CFBF) format and begins with the same D0 CF 11 E0 magic bytes. There is no .wbk-specific file signature; the extension alone distinguishes it. Renaming a .wbk to .doc is usually enough to open it in Word directly.
.wbk backups can be opened with Microsoft Word or LibreOffice Writer. The backup option and file format have remained consistent from early versions of Word through Microsoft 365.
Security & safety
RISK: LOWA .wbk is just a copy of your own document, so it carries the same low risk as the source Word file - the only real caution is the standard one: if the original document contained macros, the backup does too, so heed Word's macro warning. Don't delete .wbk files until you've confirmed the live document opens and is intact, since the backup may be your only earlier copy. Avoid 'WBK recovery/converter' download sites - Word and the free rename-to-.doc trick are all you need; third-party 'repair' tools are often PUP/adware.
Format details
in a nutshell- WordPerfect / legacy app workbook backups - A few older applications used .wbk for their own backup or workbook files, but the Microsoft Word backup is by far the dominant meaning.
Programs that open WBK files
Windows2 apps
Microsoft Word
Paid File > Open, set the file type to 'All Files (*.*)', select the .wbk and Open. If it refuses, rename the copy to .doc/.docx first. 
LibreOffice Writer
Open-source Free alternative: rename the .wbk to .doc, then open it in Writer; it reads the Word document and can export to .docx/PDF. 
macOS2 apps
Microsoft Word for Mac
Paid File > Open, choose 'All Files', select the .wbk; or rename it to .doc and double-click. Technical details
deep spec| File category | Backup copy of a Microsoft Word document |
| Container format | OLE2 Compound File Binary (CFBF) for .doc-based source files |
| Magic bytes | D0 CF 11 E0 A1 B1 1A E1 at offset 0 - identical to .doc; no .wbk-specific signature |
| Encoding | Binary |
| Byte order | Little-endian |
| Compression | None in the classic binary form |
| MIME type | application/msword |
| Typical file size | 20 KB - several MB (proportional to source document) |
| Internal structure | Byte-for-byte copy of the Word document as it existed before the most recent save |
| Naming convention | Backup of <document name>.wbk |
| Creation trigger | Created automatically on each save when 'Always create backup copy' is enabled in Word Options |
| Encryption | Inherits any password protection of the source document; otherwise unencrypted |
| Associated platforms | Windows, macOS (Word for Mac) |
| Recovery method | Rename to .doc to open directly in Word, or open via File > Open in Word or LibreOffice Writer |
| Released | Microsoft Word for Windows (early 1990s); 'Always create backup copy' option persists through Microsoft 365 Word |
| Latest version | No separate spec - mirrors whatever Word document format produced it (DOC binary or, for newer files, a Word document body) |
| Specification | support.microsoft.com |
WBK conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about WBK files.
