Right-click the .DAT file, select Open with > Choose another app, and pick Notepad: if the text is readable, you are done, and if it shows symbols, the file is binary and belongs to a specific program.
This guide covers what .DAT files contain, five ways to open them, how to read winmail.dat email attachments, and fixes for files that will not open.
The fastest way to read a .DAT file
A .DAT extension says only that a file holds data. Notepad tells you in seconds whether that data is text you can read or binary data for another program.
- Open File Explorer and find the .DAT file.
- Right-click the file and select Open with > Choose another app.
- Select Notepad from the list of apps.
- Read the contents. Words, numbers or comma-separated columns mean the file is plain text and you can read it right there.
- If you see scrambled symbols instead, close Notepad without saving and use the table below to find the right tool.
Never save a binary .DAT file from Notepad. Saving can change bytes the owning program depends on.
Which method should you use?
| What you have | Use this | Why |
|---|---|---|
| A .DAT file of unknown origin | Notepad (Method 1) | Shows at once whether it is text or binary |
| Notepad shows symbols and you need to know the real format | A hex editor or Format-Hex (Methods 2 and 5) | The first bytes often reveal the true file type |
| A .DAT file that sits in a program's or game's folder | The program that created it (Method 3) | Only that program understands its layout |
| A .DAT file with rows of values separated by commas or tabs | Excel's text import (Method 4) | Turns the data into columns you can sort and filter |
| An email attachment named winmail.dat or ATT00001.dat | Ask the sender to resend in HTML or plain text | The attachment is Outlook formatting data, not a document |
| Video files named .DAT inside an MPEGAV folder on a disc | VLC media player | Video CD tracks are MPEG-1 video that VLC plays |
Understanding .DAT Files
A .DAT file is a generic data file, and no single program owns the extension. The same three letters can hold plain text, program settings, game assets, video or email formatting.
Microsoft notes that changing a file name extension does not convert the file to another format. Renaming a .DAT to .mp4 or .docx only helps when the data already is that format.
| Common use of .DAT | Where you find it | What is inside | How to open it |
|---|---|---|---|
| Exported or logged data | Downloads, instrument or software export folders | Plain text, often comma- or tab-delimited | Notepad, or import into Excel |
| Program and game data | The app's or game's install or AppData folder | Binary data in a layout only that program reads | Leave it for the program; view with a hex editor only |
| Email attachment (winmail.dat, ATT00001.dat) | Messages sent from Outlook in Rich Text format | TNEF-packaged formatting, embedded objects and sometimes the real attachments | Ask the sender to resend in HTML or plain text |
| Video CD tracks | The MPEGAV folder on a Video CD | MPEG-1 video and audio | VLC media player |
.DAT files matter because programs store their working data in them. Deleting or editing one can reset settings, break a save, or stop an app from starting.
How to Open .DAT Files in Windows: Method 1, Using a Text Editor
Notepad ships with Windows 11 and Windows 10 and opens any file as text. Use it first on every .DAT file you did not create yourself.
- Turn on extensions so you can see the real name: in Windows 11 File Explorer select View > Show > File name extensions.
- Right-click the .DAT file and select Open with > Choose another app.
- Select Notepad and open the file.
- Read the text, or press Ctrl + F to search for a word or value.
- Close Notepad without saving if the file belongs to a program.
Readable headings, key=value lines or XML tags point to a settings or log file. Rows split by commas or tabs point to exported data that Method 4 turns into a spreadsheet.
Method 2: Using a Hex Editor
A hex editor shows every byte of a binary file without changing it. Microsoft publishes a free Hex Editor extension for Visual Studio Code that adds this view.
- Install Visual Studio Code from code.visualstudio.com.
- Open the Extensions view in Visual Studio Code, search for Hex Editor, and install the one published by Microsoft.
- Press F1 to open the Command Palette and select Open File using Hex Editor.
- Browse to the .DAT file and open it; files already open in the editor can be switched with Reopen With > Hex Editor.
- Read the right-hand text column: readable strings near the top often name the program or format that wrote the file.
If the .DAT file sits in a folder you opened in Visual Studio Code, right-click it and select Open With > Hex Editor instead.
Method 3: Using the Application that Created the File
Binary .DAT files are read correctly only by the program that wrote them. The file's folder usually tells you which program that is.
- Open the folder that holds the .DAT file in File Explorer and read the path in the address bar.
- Match the folder to a program: a path inside a game or app folder means that program owns the file.
- Open that program and use its own Open or Import command, if it has one, instead of double-clicking the file.
- If no program on your PC fits, select Start, type Microsoft Store, press Enter, then type the file extension and press Enter to see apps that handle it.
- To try an installed app, right-click the file and select Open with > Choose another app, then pick the app.
Method 4: Convert the .DAT File
A text .DAT file full of delimited values becomes a spreadsheet through Excel's text import. The original .DAT file is left unchanged.
- Right-click the .DAT file, select Copy, then paste the copy into the same folder.
- Rename the copy so it ends in .txt instead of .dat, and confirm the change.
- In Excel, click the cell where the data should start and select Data > From Text/CSV.
- Double-click the .txt copy and select Import.
- Pick the character that separates the values from the Delimiter list and check the preview.
- Select Load to place the data on a new worksheet, then use File > Save As to keep it as an Excel workbook or .csv file.
This works only for text data. Renaming a binary .DAT file does not convert it, and Excel will show the same symbols Notepad did.
Method 5: Use Command Line Tools
PowerShell can print the start of a large .DAT file without loading all of it into an editor. Open Windows Terminal or PowerShell in the file's folder first.
Get-Content -Path .\file.dat -TotalCount 20Prints the first 20 lines of file.dat. Replace file.dat with your file name and wrap names that contain spaces in quotation marks. For raw bytes, run Format-Hex -Path .\file.dat instead; in PowerShell 7, add -Count 64 to show only the first 64 bytes.
You should see: Readable lines mean a text file. Format-Hex prints offset, byte and ASCII columns, and the ASCII column on the first row often shows a format signature such as %PDF.
In Command Prompt, type file.dat | more shows a text file one screen at a time. Microsoft advises against using type on binary files because it prints control characters.
Extracting Data from winmail.dat and ATT00001.dat Email Attachments
Outlook sends winmail.dat when a message uses Rich Text format and the recipient's mail system cannot read Microsoft's TNEF packaging. Mail apps that do not recognise the winmail.dat name save the same data as ATT00001.DAT or a similar name.
The attachment holds formatting, embedded objects and sometimes the real attached files. The reliable fix is on the sender's side, so forward these steps to them.
- Ask the sender to open the message they sent, or a reply to it, in Outlook.
- On the Format Text tab, the sender selects Message Format and chooses HTML or Plain Text.
- The sender re-attaches the files and sends the message again.
- To stop it for every message, the sender selects File > Options > Mail.
- Under Compose messages in this format, the sender selects HTML or Plain Text, then OK.
Microsoft 365 admins can also turn off TNEF for mail sent to a specific outside domain with Set-RemoteDomain -Identity <Name of Domain> -TNEFEnabled $false in Exchange Online PowerShell.
How to check you opened the file the right way
- Confirm the extension is really .DAT: in Windows 11 File Explorer select View > Show > File name extensions; in Windows 10 select the View tab and tick File name extensions.
- Open the file in Notepad and check for whole words and line breaks rather than blocks of symbols.
- For a binary file, run
Format-Hex -Path .\file.datin PowerShell and read the first row of the ASCII column for a format name. - For a spreadsheet import, check that each value landed in its own column in Excel's preview.
- For a program's data file, start the program and confirm your settings, saves or content still load.
Use Cases: Opening Game .DAT Files Safely
Copy a game's or app's .DAT file to another folder before you open it anywhere, and inspect the copy rather than the original. Games and apps store saves, assets and settings in binary .DAT files that only they can rebuild, so one stray edit or save from Notepad can corrupt a save or stop the game from launching.
A winmail.dat file carries a privacy detail too. Microsoft states that it embeds the sender's .pst file path and sign-in name, visible to anyone who opens it in a text or binary editor; passwords are not included.
Troubleshooting Common Issues with .DAT Files
File not opening: Windows asks which app to use
No installed app is registered for the .dat extension.
- Select Choose another app in the prompt, or right-click the file and select Open with > Choose another app.
- Pick Notepad to find out whether the file is text.
- If it is binary, open it from inside the program that created it using that program's Open or Import command.
Notepad shows random symbols
The file is binary data, not text.
- Close Notepad without saving.
- Open a copy of the file in a hex editor or run
Format-Hexon it. - Look for a readable name or signature in the first bytes and open the file with the program it points to.
An email attachment named winmail.dat or ATT00001.dat has nothing useful in it
The sender's Outlook sent the message in Rich Text format using TNEF.
- Reply to the sender and ask them to resend the message in HTML or Plain Text format.
- Point them to File > Options > Mail > Compose messages in this format to change the default.
- If every message from a company arrives this way, ask their Microsoft 365 admin to disable TNEF for your domain.
The file does not show .dat, or renaming it did not help
File Explorer hides extensions, and renaming never converts data.
- Turn on File name extensions from the View menu in File Explorer.
- Check the full name: a file called video.mp4.dat is still a .DAT file.
- Rename only a copy, and only to a format the data already matches, such as .txt for text.
Frequently Asked Questions
How do I open and read a .DAT file?
Right-click the file, select Open with > Choose another app, and choose Notepad. Readable text means you can read it there. Symbols mean the file is binary, so open it with the program that created it or view it in a hex editor instead.
How do I read a .DAT file in Windows without extra software?
Use Notepad for text, and PowerShell for everything else. Get-Content -Path .\file.dat -TotalCount 20 prints the first 20 lines, and Format-Hex -Path .\file.dat shows the raw bytes along with any readable text they contain.
Where do I open a .DAT file, and which program should I use?
Start in the folder where the file lives. A .DAT file inside a game or app folder belongs to that program; an email attachment named winmail.dat comes from Outlook; a .DAT file in an MPEGAV folder is Video CD video that VLC plays.
How do I open a winmail.dat file?
The practical fix is to ask the sender to resend the message in HTML or Plain Text format from Outlook. Winmail.dat holds Outlook's TNEF formatting data, and Microsoft notes it has no useful information when opened in a mail app that does not support TNEF.
Can I convert a .DAT file to another format by renaming it?
Only when the data already is that format. Microsoft states that changing an extension does not convert a file. Renaming a copy of a text .DAT file to .txt or .csv works, while renaming a binary file just produces a file no app can open.
How do I open a .DAT file in Excel?
Copy the file, rename the copy to .txt, then use Data > From Text/CSV in Excel and select Import. Choose the right delimiter in the preview and select Load. This only works when the .DAT file contains text values in rows.
Is it safe to delete or edit .DAT files?
Not when a program owns them. Apps and games keep settings and saves in .DAT files, and deleting or editing one can reset settings or corrupt a save. Work on a copy, and leave the original in place.
Other uncommon formats follow the same logic. See how to open AAE files on Windows 11 and how to open DMG files on a Windows PC.
