What Is a DRMX File? A Drumlin PDF That Needs a Code to Open

2 How Do You Know Your File Is a DRMX File? No public header exists, so rule out the lookalikes

Our earlier page on this site listed 7b 44 52 4d 50 44 4b 7d, the text {DRMPDK}, as the signature of DRMX files. We could not find that header in any Drumlin document. FileInfo, FILExt, file.org and file-extensions.org list no signature at all, so we removed the claim.

We also tested the idea. We put the text {DRMPDK} in front of an encrypted blob and saved it with the ending .drmx. None of seven readers opened it, and the file command called it data. A header proves nothing about DRMX files unless Drumlin publishes it.

The chart sorts files by their first bytes. Files that start with %PDF- are PDFs, and those with the text /Encrypt inside have Adobe-style rules. Files that start with a ZIP, compound file, 7z, gzip, bzip2, xz or OpenSSL header are that kind of file. The last box is for files with no known header and a high entropy score. Genuine DRMX files may land there, and only Javelin can say.

The script below checks the first bytes and the entropy of the first 64 KB. Entropy is a score from 0 to 8 bits per byte. Text scores low, and encrypted data scores close to 8. Save it as check_drmx.py and give it the name of your DRMX file.

import math, sys
from collections import Counter

SIGNS = [
    (b'%PDF-', 'PDF'),
    (b'PK\x03\x04', 'ZIP package'),
    (b'\xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1', 'compound file'),
    (b'7z\xbc\xaf\x27\x1c', '7z archive'),
    (b'\x1f\x8b', 'gzip file'),
    (b'BZh', 'bzip2 file'),
    (b'\xfd7zXZ\x00', 'xz file'),
    (b'Salted__', 'OpenSSL file'),
]


def entropy(data):
    n = len(data)
    return -sum(c / n * math.log2(c / n) for c in Counter(data).values()) if n else 0.0


def check(path):
    data = open(path, 'rb').read()
    head = data[:8].hex(' ')
    if not data:
        return 'empty file', head, 0.0
    bits = entropy(data[:65536])
    at = data[:1024].find(b'%PDF-')
    if at >= 0:
        kind = 'PDF' if at == 0 else 'PDF with extra bytes before the header'
        if b'/Encrypt' in data:
            kind += ' with a password or rules (Adobe style)'
        if b'%%EOF' not in data[-1024:]:
            kind += ', no end marker (cut off?)'
        return kind, head, bits
    for sig, name in SIGNS:
        if data.startswith(sig):
            return name, head, bits
    if bits > 7.5:
        return 'unknown binary, no known header (looks encrypted)', head, bits
    return 'unknown, low entropy (maybe text)', head, bits


if __name__ == '__main__':
    for p in sys.argv[1:]:
        kind, head, bits = check(p)
        print(f'{p}\n  first 8 bytes: {head}\n  entropy: {bits:.2f} bits per byte\n  verdict: {kind}')

report.drmx
  first 8 bytes: 25 50 44 46 2d 31 2e 34
  entropy: 6.84 bits per byte
  verdict: PDF

sealed.drmx
  first 8 bytes: b1 bb 9c af 1e aa e9 5f
  entropy: 7.97 bits per byte
  verdict: unknown binary, no known header (looks encrypted)

locked.drmx
  first 8 bytes: 25 50 44 46 2d 31 2e 37
  entropy: 6.76 bits per byte
  verdict: PDF with a password or rules (Adobe style)

We tried the script on all 36 stand-in files. It named 35 of them right. The one miss was a PDF with its first 8 bytes zeroed. The script cannot confirm DRMX files. It can only say when your file is something else.

Four more clues about your DRMX file

3 How Does a DRMX File Work? The file travels one way and the code another

Think of concert tickets. Paper is easy to copy, but the gate checks the barcode against a list and lets one person in. DRMX files are the tickets, Drumlin's server is the list and Javelin is the gate.

The steps in the figure come from Drumlin's offline software page, its FAQ page and its Publisher guide. The publisher converts the PDF on a Windows PC. Only control data goes to the server: the file name, the user ID, the rules and security details. The source PDF stays on the publisher's PC unless the publisher asks Drumlin to convert and host it.

The FAQ says Drumlin Publisher creates a DocID for every converted DRMX file. The DocID is stored on the DRM server and encrypted inside the file. Codes are made ahead of time for every DocID, with use counts that are often 1 or 2. When you enter a code, the server checks that it is valid, in date and active. It then authorizes your device and lowers the count.

The offline page adds that codes have no encryption or decryption role. They are look-up entries only. The FAQ says DRMX files stay encrypted and the device is what gets authorized. So the code works like a ticket check and not like a password inside the file.

After that first check, the pages show from memory. The FAQ says Javelin handles documents in memory, so no unencrypted file lands on disk. The offline page describes no further online checks once a file is authorized.

The 256-bit claim

The Publisher guide calls DRMX and DRMZ files "proprietary 256-bit encrypted formats." It does not name the algorithm or say how the encryption is set up. The home page says only "strongly encrypted PDFs." We cannot check either claim, because no public document describes the format.

The offline page calls the system mainly a deterrent for copyright and says no such system fully stops a determined attacker. That is an honest limit, and it shapes this page: we explain how the system works and how to open files, and we do not cover ways around it.

4 What Can the Publisher Control in a DRMX File? Dates, views, printing, screen capture and watermarks

The rules make DRMX files different from ordinary PDFs. They are set in Drumlin Publisher and enforced by the Javelin reader and the DRM server. The table lists the rules we found in the FAQ and the Publisher guide.

The Publisher guide lists start dates, end dates and "expires after" periods. The FAQ explains the difference. Absolute end dates work like a closing day for every reader. "Expires after" works like a rental that starts when you enter your code, and new or re-enabled codes renew it.

Notes and highlights you add in Javelin are not saved in DRMX files. The FAQ says they live in separate files and may be lost if the publisher reissues a document with a different DocID. On Windows, Create Backup Copy saves the document with its notes.

12 What Else Looks Like a DRMX File? .drmz, .drm and endings that mislead

Anyone can change the ending of DRMX files. This table lists endings that you may meet near .drmx. The FileInfo DRMZ page and the FileInfo DRM page show the neighbors.

Endings that mislead

We saved 36 files under .drmx. Eighteen of them opened in at least one tool: 13 PDFs and 5 containers. A program that trusts the ending would treat all 36 as DRMX files. The FILExt page gives the same advice we follow: look at the header bytes in a hex viewer. It says encrypted binary points to DRM, PK points to a ZIP archive and %PDF points to a PDF.

Sources also disagree on platforms. file-extensions.org lists Windows only. file.org lists Windows programs that users submitted. FileInfo adds Javelin for Mac, and Drumlin's Mac page confirms it. When a directory page conflicts with Drumlin, trust Drumlin.

Other ways to lock a PDF

Adobe-style protection puts a password or rules inside a normal PDF, and DRMX files work in another way. Drumlin advises publishers to avoid it in source files. The guide to ordinary PDF files explains the ordinary format, and the guide to DRMZ files covers the sister format.

13 What Is the DRMX File Format Made Of? The few facts we could check, and what no document says

About the values we list

The facts come from Drumlin's pages, from FileInfo, FILExt, file.org, file-extensions.org and Wikipedia, and from our own 36 stand-in DRMX files. We read them in October 2026. Drumlin's pages show few dates, so a rule may have changed since. The Wikipedia article cites Drumlin's downloads page and gives no release dates either.

The file.org page says the DRMX ending shows your device which app can open the file. It warns that different programs may use the same ending. That fits what FileInfo shows for .drm.

What we left out

We did not test Drumlin Publisher, Javelin on any system, Apple silicon, mobile readers, JavelinPro, license files, self-authorizing DRMZ files or the "Click and Go" EXE. We also left out the old {DRMPDK} header, because we found it in no Drumlin document.

Our stand-in DRMX files are not made by Drumlin. We tried seven readers, and others may behave in other ways. We name no converter or viewer other than Drumlin's own, because we found none that we could check. We name no prices.

Sources checked

For the formats and the system, see the Drumlin offline software and services page, the Drumlin FAQs, the Drumlin Mac page and the Publisher guide PDF. Also see the Drumlin home page. For the extension, see FileInfo for DRMX, FILExt, file.org and file-extensions.org. For the reader, see the Wikipedia article on Javelin. For media types, see the IANA registry.

Every test count came from the 36 stand-in files and the scripts in our research folder.