File Formats
What Is DOC? The Word 97-2003 Binary Format
DOC is the binary document format Word used from Word 97 to Word 2003, and it still turns up in many archives. Here is how it works inside, where it falls short and how to convert it safely.
Author: Hemen Dönüştür Editör EkibiPublished: 7 min read
Dig into an organization's old archive, scroll to the bottom of a long email thread, or export a report from software that has not been updated in years, and you will run into files ending in .doc. DOC was Microsoft Word's default format until DOCX arrived with Word 2007, and a great many documents still exist in it. This article explains where DOC came from, how it is organized internally, why it differs from DOCX, and how to open and convert these files safely.
What is DOC?
DOC is Microsoft Word's binary document format. Today "DOC" usually means the format shared by Word 97, 2000, 2002 (XP) and 2003, and Microsoft's official specification covers exactly those versions. Unlike text-based formats, opening a DOC file in Notepad shows nothing meaningful: the content is a sequence of bytes laid out according to Word's own data structures.
A short history
The ".doc" extension was first used in 1983 with the MS-DOS version of Word. The extension stayed the same, but the format behind it changed several times:
- Word for Windows 1.0 and 2.0: used their own DOC format.
- Word 6.0 and Word 95: the format changed, and these two versions shared it.
- Word 97 to Word 2003: DOC was rebuilt on OLE and the Compound File Binary Format (CFB). Microsoft also released an import converter so Word 6.0 and 95 users could open the new files.
- Word 2007: DOCX became the default. Word kept opening and saving DOC; when you open one, the title bar shows "Compatibility Mode".
Documentation of the format has its own long story. In 1997 Microsoft published the Office 97 binary format specifications under a restrictive license and withdrew them in 1999. From 2006 until February 2008 the specification was only available on request under restricted terms, so projects such as OpenOffice.org had to reverse engineer the format. In February 2008 Microsoft released the DOC specification under its Open Specification Promise. The document now published on Microsoft Learn as [MS-DOC] lists its first version as June 27, 2008, and it is still maintained: the most recent revision listed on the page is dated February 17, 2026.
What is inside a DOC file?
A post-Word 97 DOC file is really a "file system inside a file". According to Microsoft's [MS-CFB] specification, the Compound File Binary Format provides a file-system-like structure within a file for storing application-specific streams of data. Folders are called storages and files are called streams. The file is divided into fixed-size sectors (512 bytes in version 3, 4096 bytes in version 4), and an allocation table (FAT) tracks which sector belongs to which stream.
Every compound file begins with the same 8-byte signature:
D0 CF 11 E0 A1 B1 1A E1That signature is not specific to Word; legacy Excel (.xls) and PowerPoint (.ppt) files use the same container. What makes a DOC file a Word document is the set of streams inside it:
- WordDocument stream: holds the document text and, at offset 0, the FIB (File Information Block). The FIB works like a table of contents that points to where everything else lives.
- Table stream (0Table or 1Table): carries the data the FIB points to, such as formatting, styles, fonts and paragraph properties. Per MS-DOC, the
fWhichTblStmbit in the FIB decides which one is used; if both exist, the unreferenced stream is ignored. - Data stream: may hold additional data such as embedded pictures.
- ObjectPool storage: stores embedded OLE objects, for example an Excel table.
- SummaryInformation streams: summary metadata such as title, author and creation date.
If the document is encrypted, the table stream starts with an encryption header. This complex, pointer-based layout let DOC files load quickly, but it also meant that a single damaged sector could make a whole document unreadable, and that other software found the format hard to implement correctly.
DOC vs DOCX
| Feature | DOC | DOCX |
|---|---|---|
| Structure | Binary, OLE2 compound file | XML parts inside a ZIP |
| Standard | Microsoft-published specification (MS-DOC) | ECMA-376 and ISO/IEC 29500 |
| Macros | Can carry VBA macros in the same file | Cannot (macro-enabled documents use .docm) |
| Resilience | Low, a single error can affect the whole file | Higher, parts can be read independently |
| Newer Word features | Some post-2007 features have no equivalent | Full support |
Where do you still find DOC?
- Corporate and public archives: correspondence, reports and templates created before 2007.
- Legacy software: accounting, HR or industry tools that still export reports as DOC.
- Upload systems: old web forms and internal systems that only accept DOC.
- Macro templates: forms and templates with automation built years ago.
Strengths and weaknesses
Strengths: very broad software support; nearly every word processor since Word 97 opens DOC. Because it has been around for so long, it is the Word format least likely to cause trouble with old systems.
Weaknesses: because of its closed history, complex documents can lose their layout in third-party applications. Since it can carry macros, it is riskier than DOCX from a malware point of view. Some features added after Word 2007, such as newer graphics and layout elements, are simplified or lost when saved as DOC. Files are also usually larger than a DOCX with the same content.
Which programs open DOC?
Every desktop version of Microsoft Word opens DOC. LibreOffice Writer, Google Docs, Apple Pages and WPS Office can read it as well. On Linux servers and in automation workflows, DOC files are usually processed with LibreOffice.
Common problems and how to fix them
Word opens the file in Protected View and I cannot edit it
Word opens legacy files from the internet or email as read-only for security. If you trust the source, click "Enable Editing". Do not enable macros in documents from unknown sources that ask you to.
The file will not open or shows garbage characters
Some .doc files are not really DOC. Word's "Save as Web Page" output and renamed RTF or DOCX files can travel with a .doc extension. Try a program that detects content, such as LibreOffice. For a genuinely damaged DOC, Word's "Open and Repair" option may recover the text.
Compatibility Mode and missing features
Newer Word features are unavailable in a document saved as DOC. If you will keep editing it, convert it to DOCX with "File > Info > Convert".
Tips for converting DOC files
On our converter, DOC files are uploaded to our server, processed with LibreOffice and deleted within 30 minutes. Before converting, the first bytes of the file are checked: genuine DOC files, ".doc" files that are actually DOCX or RTF, and Word's HTML-based ".doc" output are all accepted. If the content matches none of these, you get a "file could not be read" message instead of a document full of garbage.
- DOC to Word (DOCX) is the best way to keep old documents alive. The conversion runs directly through LibreOffice with no intermediate step, so page layout, headers and footers, tables and images are preserved.
- DOC to PDF suits archiving or sharing with someone who does not have Word.
- DOC to UDF first normalizes the document to DOCX and then maps it to the UYAP format.
- DOC to TXT extracts only the plain text, which is handy for searching an old archive or feeding another system.
- If you need to upload a DOCX to a legacy system, use Word to DOC.
Frequently Asked Questions
Should I still use the DOC format?
Not for new documents; DOCX is safer, more robust and an open standard. Use DOC only when the receiving system accepts nothing else.
Can a DOC file contain a virus?
DOC files can contain VBA macros, and macro viruses can spread that way. Do not enable macros in DOC files from unknown sources, and keep your office software up to date.
Do I lose anything converting DOC to DOCX?
Usually not. DOCX covers nearly everything DOC supports. Some field codes or embedded objects specific to very old Word versions may look different, so review important documents after conversion.
Is the DOC specification public?
Yes. Microsoft publishes the Word 97-2003 binary format as [MS-DOC] and the compound file container as [MS-CFB] on Microsoft Learn. Since February 2008 these specifications have been covered by the Open Specification Promise.
Can I open a DOC file on my phone?
The Word mobile app and Google Docs can open DOC. If you only need to read it, converting it to PDF guarantees it displays correctly on any device.
