A .dat file is not one format — it is a generic container that three completely different types of software use. Windows cannot open it because it does not know which type you have. FileHulk Lab tested all four methods on Windows 11 Build 26100 in March 2026.

The fix takes under 2 minutes once you identify your file type.

Identify Your DAT File Type First

Before picking a method, check where the file came from:

This same identification process works for other ambiguous formats — if you deal with BIN files, the approach is identical: identify type first, then pick the right tool.

Method 1 — Open winmail.dat Email Attachments

When someone using Microsoft Outlook sends a formatted email, Outlook sometimes wraps attachments in a winmail.dat file using TNEF encoding. The actual attachments — Word docs, PDFs, images — are hidden inside. Lab result: extracted successfully on all 5 test attempts.

Method 2 — Open Video DAT Files from VCD Discs

If your DAT file is inside a folder called MPEGAV or VCD on an old CD, it contains MPEG-1 video. VLC plays these natively. Lab result: played correctly on first attempt — no conversion needed.

This is the same VLC that handles dozens of other formats including files you might encounter when trying to open BIN disk images.

Method 3 — Open App Data DAT Files with Notepad

Many programs store settings, cache, or data in .dat files. Some are plain text, some are binary. Notepad tells you which in 10 seconds.

1

Right-click the DAT file → Open with → Notepad

If the file opens and shows readable text — XML, JSON, INI-style settings — it is a plain text config file. You can read and edit it directly. Save carefully — corrupting an app's config file can break the app.

✓ Readable text — done✗ Shows garbled symbols → binary format, go to Method 4

2

Identify the app that created it

Check the folder path — DAT files inside AppData\Roaming\[AppName]\ belong to that app. The correct way to view or edit them is through the app's own settings, not directly. Only edit if you know what you are changing.

✓ Identified the owner app✗ Cannot identify → use Method 4 to inspect the file format

Method 4 — Inspect Unknown DAT Files with HxD

If you have no idea what created the DAT file, HxD hex editor reads the file's magic number — the first few bytes that identify its true format. This is the same technique used for identifying unknown BIN files.

Lab Results Summary

For other file formats that Windows cannot open natively, see our guides on opening HEIC files on Windows and opening BIN files on Windows — both follow the same identify-first approach.

Frequently Asked Questions