DjVu file signature
Magic number at the start of the file · AT&TFORM
DjVu scanned documents use an IFF container tagged AT&T. The file starts with AT&T then FORM, and a form type of DJVU (single page) or DJVM (multi-page) follows.
What this magic number means
A magic number is a short, fixed run of bytes at a known position that tells a program what a file really is, no matter what the filename says. If a file starts with the bytes 41 54 26 54 46 4F 52 4D (the text AT&TFORM), it is a DjVu file.
Formats that use the 41 54 26 54 signature
These file types in our database carry this signature:
How to check a file's signature
You can read the first bytes of any file yourself. The magic bytes are shown in hex, the same way this page lists them.
Linux & macOS
- xxd -l 16 example.djvu
- hexdump -C -n 16 example.djvu
- file example.djvu
Windows (PowerShell)
- Format-Hex -Path example.djvu -Count 16
Python
- open("example.djvu","rb").read(8).hex()
In your browser
- Drop the file into the WhatFileType identifier, which reads the signature without uploading it.
Frequently asked questions
What is the DjVu file signature?
DjVu files start with the hex bytes 41 54 26 54 46 4F 52 4D (AT&TFORM in ASCII). This magic number identifies the format regardless of the file's name or extension.
How do I check a file's magic number?
Open the file in a hex editor, or run a command such as xxd -l 16 example.djvu on Linux or macOS, or Format-Hex -Path example.djvu -Count 16 in Windows PowerShell, and read the first bytes.
Can a file fake the DjVu signature?
Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine DjVu file has these exact bytes; a file with the wrong bytes is not really DjVu, whatever its name says.