Welcome to the Microsoft Answers Forum. Usually.dat files can be open with Notepad or with Microsoft Word. Have you tried using any of these? Just save the.dat file to a destination of your choice and right click on it and click Open with and choose either notepad or Winword, if you only see the choice to just use Open when you right click.
So you just received an email with an attachment that someone sent you, but the extension on the file is .DAT. What exactly is a .DAT file and how to you open .DAT files? These are two questions I’m going to try to answer as I’ve seen many friends and family encounter this problem before.
The first thing to understand about .DAT files is that it indicates a file that has arbitrary data. That means it’s not associated with any one particular program or application. When you see a file with a .XLS extension, you know it’s referring to an Excel file, and so on. But with .DAT files, you have to figure out how to open it yourself and different .DAT files may open with different programs.
Before we get into the different ways you can open a DAT file, it’s worth noting that you should first check to make sure the file does not contain any viruses. Since a DAT file can be anything, I’ve seen cases where spammers and hackers try to hide spyware or viruses inside DAT files.
If you don’t already have an anti-virus program, I recommend using either Kaspersky or Bitdefender since they consistently perform at the top in AV-Test and AV-Comparatives rankings. They are not free, but most free antivirus programs end up bundling extra junk software or redirecting your browser to their “secure” search solution, which isn’t secure at all and just tracks you and shows you more ads.
The best way to open a .DAT file is to use the program that created it. Obviously, that’s easy if you knew which program created it, right? So how does one go about figuring this out? Well, there are a couple of ways. Firstly, you can try opening the file in something like Notepad. You should know that Notepad can open anything, even image and video files and display them as text.
Almost all of the file will most likely be gibberish that makes no sense, but sometimes at the beginning or end of the file, you will see some useful information. This is because even videos, images, etc have some sections of the file that are text and that usually contain information about the file. As an example, I opened the Wildlife sample video in Windows 7 using Notepad.
When opening the file in Notepad, you need to choose All Files otherwise it will only show you text files. Once you do this, select the video file and open it. It might take a while to open it if it’s a big video file. Now look at the top and you’ll see some interesting info:
As you can see, there is some text and even though it doesn’t tell you the exact filetype, you can gather that it’s a video file from Microsoft. My first choices would be WMV (Windows Media Video) or AVI. Now Notepad is a very simple tool and it may not work all the time depending on what kind of file it is.
However, I have written another post on how to determine the filetype of a file that doesn’t have an extension and the same procedure that I describe there can be used to for DAT files. Basically, you have to install a hex editor, which lets you view the hex code for a file and more accurately see the data. You’ll have a much better chance of figuring out the original file type using this method.
You’ll normally only see DAT files when receiving emails with attachments. Most common programs today do not generate .DAT files and only computer programmers use these files on any kind of regular basis.
Another thing you could try would be to ask the person who sent you the email if they know which program was used to create the file. Now if they tell you that they actually sent a picture or a document and they are not sure why it’s a .DAT file, it could be that the file extension was changed in the process of having the email routed to you.
For some strange reason, some email programs automatically change the file extension on email attachments to .DAT. So if the person sent you a picture and now it’s a .DAT file, you first need to save it to your computer and then change the file extension to JPG or GIF or PNG or whatever you think it’s supposed to be. If they sent you a Word document, change it to .doc or .docx, etc.
You can change the file extension on a file by first going to My Computer, clicking on Tools and then Folder Options.
In Windows 7, you have to click on the Organize button and then click on Folder and Search Options.
In Windows 8, click on the View tab and then check the File name extensions box.
Except for Windows 8, you’ll need to click on the View tab next and then scroll down to the option “Hide extensions for known file types” and UNCHECK it. In this way, we’ll now be able to see the file extension and change it to something else.
Now simply right-click on the .DAT file and change the file extension after the dot to the desired file format. You should also see the icon representing the file change to the appropriate program used to open that file type, i.e. Excel in the screenshot below.
If you’re still not able to determine the file type using Notepad or the hex editor, you can go at it with a brute force attack. Basically, right-click on the DAT file, choose Open With and try as many programs as you can find. For testing, I changed one of my Excel files to a .DAT extension, right-clicked on it, choose open with Excel and it worked!
Now Windows was actually smart enough to figure out that the file was an Excel file even though the extension was incorrect because it gave me Excel as the top recommended program.
You should also try programs like VLC for any type of possible video or music file and a photo viewer in case it’s an image, etc. So hopefully you are now able to open your mysterious .DAT file using one of the above-mentioned methods! If not, post a comment and I will try to help! Enjoy!
Outlook saves backup information in a variety of different locations. Depending on what type of account you have, you can back up your emails, your personal address book, your navigation pane settings, your signatures, templates, and more.
If you're using a Microsoft Exchange, Office 365, or Outlook.com account, your email messages are backed up on your email server. In most cases, you won't have a Personal Folders file (.pst) for these types of accounts.
In order to view some of the backup files for Outlook, you'll need to unhide system folders and file name extensions. For information on how to perform that task, see How to unhide folders and file name extensions.
Backup information for Office 365, Exchange, or Outlook.com accounts
For Office 365 accounts, Exchange accounts, or Outlook.com, Hotmail.com, or Live.com accounts not accessed by POP or IMAP, you won't have a Personal Folders (.pst) file. You may have an Offline Folders (.ost) file, but that file is automatically recreated by Outlook when you add a new email account. You can't move that file from one computer to another.
For Office 365 accounts, Exchange accounts, or Outlook.com, Hotmail.com, or Live.com accounts not accessed by POP or IMAP, the following information can be transferred from one computer to another.
Navigation Pane settings
You can find these settings in one of the following locations:
Windows 10 drive:Users<username>AppDataRoamingMicrosoftOutlookprofile name.xml
Older versions of Windows drive:Documents and SettingsuserApplication DataMicrosoftOutlookprofile name.xml
Print styles
You can find the Outlprnt file in one of the following locations:
Windows 10 drive:Users<username>AppDataRoamingMicrosoftOutlookOutlprnt
Older versions of Windows drive:Documents and SettingsuserApplication DataMicrosoftOutlookOutlprnt
Signatures
You can find the various files that make up your Outlook signatures in one of the following locations:
Windows 10 drive:Users<username>AppDataRoamingMicrosoftSignatures
Older versions of Windows drive:Documents and SettingsuserApplication DataMicrosoftSignatures
Stationery
Stationery can be stored in two different locations depending on whether you have the 32-bit or 64-bit version of Outlook installed. You can find the various files that make up your Outlook stationery in one of the following locations:
All versions of Windows drive:Program FilesCommon FilesMicrosoft SharedStationery
All versions of Windows drive:Program Files (x86)Common Files Microsoft SharedStationery
Custom forms
You can find the various files that make up your custom Outlook forms in one of the following locations:
Windows 10 drive:Users<username>AppDataLocalMicrosoftForms
Older versions of Windows drive:Documents and SettingsuserLocal SettingsApplication DataMicrosoftForms
Dictionary
Your custom dictionary files are stored in one of two places:
Windows 10 drive:Users<username>AppDataRoamingMicrosoftUProof
Older versions of Windows drive:Documents and SettingsuserApplication DataMicrosoftUProof
Templates
Microsoft Dat Files
Any Outlook templates you've created are stored in one of two places. Templates will have an .oft extension.
Windows 10 drive:Users<username>AppDataRoamingMicrosoftTemplates
Older versions of Windows drive:Documents and SettingsuserApplication DataMicrosoftTemplates
Send/Receive settings
Your send and receive settings include which accounts are checked at what frequency. You can find your send and receive settings file in one of the following locations. The file will have an .srs extension.
Windows 10 drive:Users<username>AppDataRoamingMicrosoftOutlook
Older versions of Windows drive:Documents and SettingsuserApplication DataMicrosoftOutlook
Email, calendar, contact, and task information for POP and IMAP accounts
If you have a POP or IMAP account, all of your information is already stored in a Personal Folders (.pst) file. You can move this file to a new computer and retain your information. Moving a .pst file from one computer to another doesn't transfer your email account settings. If you need to set up Outlook on a new computer, copy your .pst file from the old computer, then set up your email account on your new computer. You can then open the .pst file from the new computer.
The location of your .pst file depends on your version of Outlook, your version of Windows, and how you set up your account or created the .pst file. You can find your .pst file in one of the following locations:
Windows 10 drive:Users<username>AppDataLocalMicrosoftOutlook
Windows 10 drive:Users<username>RoamingLocalMicrosoftOutlook
Older versions of Windows drive:Documents and Settings<username>Local SettingsApplication DataMicrosoftOutlook
Tip: If your Outlook Data File (.pst) becomes large it can slow down your OneDrive sync and may show 'Processing changes' or 'A file is in use'. Learn How to remove an Outlook .pst data file from OneDrive.
Note: Your configuration might not include all of these files as some are created only when you customize Outlook features.
Can't find the folders?
Some of the folders might be hidden folders. To display hidden folders in Windows, do the following:
Click the Start button, and then click Control Panel.
Open Folder Options.
To locate Folder Options, in the search box at the top of window, type Folder Options. In Control Panel for Windows XP, type Folder Options in the Address box.
On the View tab, under Advanced settings, under Files and Folders, under Hidden files and folders, select Show hidden files and folders.
Outlook Data File (.pst)
Outlook Data Files (.pst) contain your e-mail messages, calendars, contacts, tasks, and notes. You must use Outlook to work with the items in a .pst file.
When you archive Outlook information, items are saved in a .pst files.
Notes:
Microsoft Exchange Server accounts save your information on the mail server. To use Cached Exchange Mode or to work offline, copies of your items are saved in an offline Outlook Data File (.ost). See the Outlook Data Files (.ost) section for more information. Also, some organizations allow you to export or archive your items to a .pst file.
Moving a .pst file to a network share is not supported. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
297019 Personal folder files are unsupported over a LAN or over a WAN link
How to identify the name and location of your personal folders file
Microsoft Outlook 2010
In Outlook 2010, click the File tab in the Ribbon, and then click the Info tab on the menu.
Click Account Settings, and then click Account Settings.
Click DataFiles.
Note the path and file name of your .pst file. For example, C:ExchangeMailbox.pst indicates a .pst file that is named Mailbox.pst and is located in the Exchange folder on your drive C.
Outlook Data Files (.pst) created by using Outlook 2010 are saved on your computer in the DocumentsOutlook Files folder. If you are using Windows XP, these files are created in the My DocumentsOutlook Files folder.
Tip: If your Outlook Data File (.pst) becomes large it can slow down your OneDrive sync and may show 'Processing changes' or 'A file is in use'. Learn How to remove an Outlook .pst data file from OneDrive.
If you upgraded to Outlook 2010 on a computer that already had data files created in previous versions of Outlook, these files are saved in a different location in a hidden folder.
Windows 7 and Windows Vista drive:UsersuserAppDataLocalMicrosoftOutlook
Windows XP drive:Documents and SettingsuserLocal SettingsApplication DataMicrosoftOutlook
Tip: For information about hidden folders in Windows, see Windows Help and Support.
Microsoft Office Outlook 2007
Start Outlook.
On the Tools menu, click Options.
On the Mail Setup tab, click the Data Files button.
Note the path and file name of your .pst file. For example, C:ExchangeMailbox.pst indicates a .pst file that is named Mailbox.pst located in the Exchange folder on your drive C.
5. Click Close, click OK, and then click Exit and Log Off on the File menu to quit Outlook.
How to copy your personal folders file
On the Start menu, point to Programs, and then click Windows Explorer.
Browse through the files to the location of your .pst file.
Copy your .pst file to the location that you want.
For more information about how to copy a file or folder, follow these steps:
Click the Start button, and then click Help.
Click the Search tab, and then type copy.
In the Select Topic to display box, click Copy or move a file or folder.
How to point Outlook to your new personal folders file
Microsoft Outlook 2010
Open Outlook 2010.
Click the File tab on the Ribbon, and then click the Info tab on the menu.
Click the Accounts Settings tab, and then click Account Settings again.
On the Data Files tab, click Add.
Under Save as type, select Outlook Data File (*.pst).
Find the new location for your .pst file, and then click OK.
Select the .pst file, and then click Set as Default.
If this is your default e-mail delivery location, you will receive the following message:
You have changed the default deliver location for your e-mail. This will change the location of your Inbox, Calendar, and other folders. These changes will take effect the next time you start Outlook.
9. Click OK.
10. Click the .pst file that was identified in the 'How to Identify the Name and Location of Your Personal Folder File' section, and then click Remove to remove the local .pst file from your profile.
11. Click Yes, click Close, and then click OK to close all dialog boxes.
12. On the File menu, click Exit.
13. Restart Outlook.
Your profile now points to your .pst file in the new location. Outlook opens your new .pst file, and you can now delete the .pst file from its old location.
Microsoft Office Outlook 2007
Open Outlook.
On the Tools menu, click Options.
On the Mail Setup tab, click the E-mail accounts button, even if you do not have an email account specified.
On the Data Files tab, click Add.
Click Office Outlook Personal Folders File (.pst), and then click OK.
Find the new location for your .pst file, and then click OK two times.
Click Set as Default.
If this is your default e-mail delivery location, you will receive the following message:
You have changed the default deliver location for your e-mail. This will change the location of your Inbox, Calendar, and other folders. These changes will take effect the next time you start Outlook.
9. Click OK.
10. Click the .pst file that was identified in the 'How to identify the name and location of your personal folder file' section, and then click Remove to remove the local .pst file from your profile.
11. Click Yes, click Close, and then click OK to close all dialog boxes.
12. On the File menu, click Exit.
13. Restart Outlook.
If the .pst is your default delivery location, you will receive the following message:
The location that messages are delivered to has changed for this user profile. To complete this operation, you may need to copy the contents of the old Outlook folders to the new Outlook folders. For information about how to complete the change of your mail delivery location, see Microsoft Outlook Help. Some of the shortcuts on the Outlook Bar may no longer work. Do you want Outlook to recreate your shortcuts? All shortcuts you have created will be removed.
Click Yes to have Outlook update the Outlook Bar shortcuts so that they point to your new .pst file location, or click No to leave the shortcuts for your original local .pst file.
Your profile now points to your .pst file in the new location. Outlook opens your new .pst file, and you can now delete the .pst file from its old location.
File (.ost)
The .ost file is synchronized with the items on the server that runs Exchange. Because your data remains on the Exchange server, you can re-create this .ost file on your new computer without having to back up the .ost file.
File Extension Dat Winmail
Windows 7 and Windows Vista drive:UsersuserAppDataLocalMicrosoftOutlook
Windows XP drive:Documents and SettingsuserLocal SettingsApplication DataMicrosoftOutlook
Personal Address Book (.pab)
Windows 7 and Windows Vista drive:UsersuserAppDataLocalMicrosoftOutlook
Windows XP drive:Documents and SettingsuserLocal SettingsApplication DataMicrosoftOutlook
Note: Personal Address Books (.pab) are not supported in Outlook 2010. When you upgrade to Outlook 2010, you are prompted to import any .pab file into Contacts. If you choose not to import the .pab file when you first run Outlook 2010, you can import it later by using the Import command in the Microsoft Office Backstage view.
Offline Address Book (.oab)
The Offline Address Book (.oab) is used by Microsoft Exchange Server accounts. It contains information, such as names, e-mail address, titles, and office locations, from the Global Address List (GAL) on the server that runs Exchange.
You do not have to back up or restore this file. This is file is created and updated automatically.
Windows 7 and Windows Vista drive:UsersuserAppDataLocalMicrosoftOutlook
Windows XP drive:Documents and SettingsuserLocal SettingsApplication DataMicrosoftOutlook
Navigation Pane settings (.xml)
This file includes information about the contents of the Navigation Pane.
Windows 7 and Windows Vista drive:UsersuserAppDataRoamingOutlookprofile name.xml
Windows XP drive:Documents and SettingsuserApplication DataMicrosoftOutlookprofile name.xml
Registered Microsoft Exchange extensions (.dat)
Windows 7 and Windows Vista drive:UsersuserAppDataLocalMicrosoftOutlook
Windows XP drive:Documents and SettingsuserLocal SettingsApplication DataMicrosoftOutlook
Outlook Contacts Auto-Complete List
The Auto-Complete List is a feature that displays suggestions for names and e-mail addresses as you begin to type them. These suggestions are possible matches from a list of names and e-mail addresses from the e-mail messages that you have sent.
In Outlook 2007, the Auto-Complete List file (.nk2) is stored in the following locations:
Windows Vista drive:UsersuserAppDataRoamingMicrosoftOutlook
Windows XP drive:Documents and SettingsuserApplication DataMicrosoftOutlook
In Outlook 2010, the Auto-Complete List file (.nk2) is discontinued. The Auto-Complete List entries are now saved in your Microsoft Exchange Server mailbox or in the Outlook Data File (.pst) for your account.
Exchange Server accounts
If you are using an Exchange Server account, your Auto-Complete List is saved in your mailbox on the server that runs Exchange. This enables your Auto-Complete List to be used from any computer that you use Outlook with your Exchange account.
How can I tell if I have a Microsoft Exchange Server account?
Click the File tab. Click Account Settings, and then click Account Settings. On the E-mail tab, the list of accounts indicates the type of each account.
POP3 accounts
The Auto-Complete List is saved in the Outlook Data File (.pst). See the section Find and transfer Outlook data files from one computer to another for location information.
IMAP and Outlook.com accounts
The Auto-Complete List is saved in the Outlook Data File (.pst). The Outlook Data Files (.pst) for these account types differ from other Outlook Data Files (.pst) in Outlook. These files are used as copies of information on your mail server account and not intended to be moved or restored. A new Outlook Data File (.pst) is created when you configure an IMAP or an Outlook.com (formerly Hotmail) account in a different Outlook profile or on another computer. Your Auto-Complete List, therefore, is unique to the computer and profile where the account is set up and the entries do not appear in any other profile or computer that you use.
Rules (.rwz)
Windows 7 and Windows Vista drive:UsersuserAppDataRoamingMicrosoftOutlook
Windows XP drive:Documents and SettingsuserApplication DataMicrosoftOutlook
Note: If you upgraded to Outlook 2010 from a version of Outlook earlier than Microsoft Outlook 2002, you might have an .rwz file on your computer's hard disk drive. The .rwz file is no longer needed, and the information about rules is now kept on the server running Microsoft Exchange, and in the Outlook Data File (.pst) for POP3 and IMAP e-mail accounts. You can delete the file.
File Extension Dat Microsoft Download
If you use the Rules Import and Export feature, the default location for .rwz files is your Documents folder.
Print styles (Outlprnt with no extension)
Windows Vista drive:UsersuserAppDataRoamingMicrosoftOutlook
Windows XP drive:Documents and SettingsuserApplication DataMicrosoftOutlook
Signatures (.rtf, .txt, .htm)
Windows 7 and Windows Vista drive:UsersuserAppDataRoamingMicrosoftSignatures
Windows XP drive:Documents and SettingsuserApplication DataMicrosoftSignatures
Stationery (.htm)
Windows 7 and Windows Vista drive:Program FilesCommon FilesMicrosoft SharedStationery
Windows 7 and Windows Vista 64-bit with Outlook 2010 32-bit drive:Program Files (x86)Common FilesMicrosoft SharedStationery
Windows XP drive:Program FilesCommon FilesMicrosoft SharedStationery
Custom forms
Windows 7 and Windows Vista drive:UsersuserAppDataLocalMicrosoftForms
Windows XP drive:Documents and SettingsuserLocal SettingsApplication DataMicrosoftForms
Dictionary (.dic)
Windows 7 and Windows Vista drive:UsersuserAppDataRoamingMicrosoftUProof
Windows XP drive:Documents and SettingsuserApplication DataMicrosoftUProof
Templates (.oft)
Windows 7 and Windows Vista drive:UsersuserAppDataRoamingMicrosoftTemplates
Windows XP drive:Documents and SettingsuserApplication DataMicrosoftTemplates
File Extension Dat_old
Send/Receive settings (.srs)
Windows 7 and Windows Vista drive:UsersuserAppDataRoamingMicrosoftOutlook
Windows XP drive:Documents and SettingsuserApplication DataMicrosoftOutlook
Message (.msg, .htm, .rtf)
Windows 7 and Windows Vista drive:UsersuserDocuments
Windows XP drive:Documents and SettingsuserMy Documents
How to unhide folders and file name extensions
Some of the folders might be hidden folders, and Windows might have file name extensions (such as .pst, .ost, .pab) turned off. To show hidden folders and file name extensions, do the following:
Open Control Panel.
In Windows 10, right-click the Start button, and then click Control Panel.
In Windows 8, press the Windows key + X, then click Control Panel.
In Windows 7, click Start > Control Panel.
In the View by list, make sure either Large icons or Small icons is selected so that you can see all the icons in Control Panel.
Click Folder Options.
Click the View tab.
In the Advanced settings box:
Under Files and Folders, uncheck the Hide extensions for known file types box
Under Hidden files and folders, click the Show hidden files, folders, and drives button.
Click OK.