Microsoft Office Open XML Format (.docx)
.docx file signature | application/vnd.openxmlformats-officedocument.wordprocessingml.document
Microsoft Office Open XML Document is a file format standardized by Ecma International and maintained through the ISO/IEC process, with implementation originating from Microsoft. It is used for word processing documents in Microsoft Word and compatible office suites, including reports, letters, manuals, and forms. The format is based on a compressed package structure and is generally safe, though documents may contain macros, embedded objects, or other active content that should be treated cautiously when opened from untrusted sources.
Magic Bytes
Offset 0
50 4B 03 04
Sources: Wikipedia
All Known Signatures
4 signature variants are documented for .docx files across multiple sources.
| Hex Signature | Offset | Sources |
|---|---|---|
| 50 4B 03 04 | 0 | Wikipedia |
| 50 4B 05 06 | 0 | Wikipedia |
| 50 4B 07 08 | 0 | Wikipedia |
| 50 4B 03 04 14 00 06 00 | 0 | Gary Kessler |
Extension
.docx
MIME Type
application/vnd.openxmlformats-officedocument.wordprocessingml.document
Byte Offset
0
Risk Level
Safe
Validation Code
How to validate .docx files in Python
def is_docx(file_path: str) -> bool:
"""Check if file is a valid DOCX by magic bytes."""
signature = bytes([0x50, 0x4B, 0x03, 0x04])
with open(file_path, "rb") as f:
return f.read(4) == signatureHow to validate .docx files in Node.js
function isDOCX(buffer: Buffer): boolean {
const signature = Buffer.from([0x50, 0x4B, 0x03, 0x04]);
return buffer.subarray(0, 4).equals(signature);
}How to validate .docx files in Go
func IsDOCX(data []byte) bool {
signature := []byte{0x50, 0x4B, 0x03, 0x04}
if len(data) < 4 {
return false
}
return bytes.Equal(data[:4], signature)
}API Endpoint
/api/v1/docx
curl https://filesignature.org/api/v1/docx
See the full API documentation for all endpoints and parameters.
Related Formats
Frequently Asked Questions
What is a .docx file?
A .docx file is a Microsoft Office Open XML Format file. Microsoft Office Open XML Document is a file format standardized by Ecma International and maintained through the ISO/IEC process, with implementation originating from Microsoft. It is used for word processing documents in Microsoft Word and compatible office suites, including reports, letters, manuals, and forms. The format is based on a compressed package structure and is generally safe, though documents may contain macros, embedded objects, or other active content that should be treated cautiously when opened from untrusted sources.
What are the magic bytes for .docx files?
The magic bytes for Microsoft Office Open XML Format files are 50 4B 03 04 at byte offset 0. These bytes uniquely identify the file format regardless of the file extension.
How do I validate a .docx file?
To validate a .docx file, read the first bytes of the file and compare them against the known magic bytes (50 4B 03 04) at offset 0. This is more reliable than checking the file extension alone, as extensions can be renamed.
What is the MIME type for .docx files?
The primary MIME type for .docx files is application/vnd.openxmlformats-officedocument.wordprocessingml.document.
Is it safe to open .docx files?
Microsoft Office Open XML Format (.docx) files are generally safe to open. They are classified as low risk because they primarily contain data rather than executable code. However, always ensure files come from a trusted source.