What Is an MDW File?

How to open, edit, & convert MDW Files

A file with the MDW file extension is a Microsoft Access Workgroup Information file, sometimes just called a WIF (workgroup information file).

It stores the usernames and passwords for users and groups that should have access to a particular MS Access database, like an MDB file. While the credentials for a database are stored in the MDW file, it's the MDB file that holds the permissions that the users are granted.

MDW files in Windows 10 that open with Access

How to Open an MDW File

MDW files can be opened with Microsoft Access.

The user-level security that the file provides are for MDB files only, so they're not available for use with newer database formats like ACCDB and ACCDE. See Microsoft's What happened to user-level security? for some additional information on that.

If Access isn't opening it, it's possible that your specific file isn't a Microsoft Access file at all. This is because other programs may use the same file extension to hold information other than database credentials like with the WIF.

For other MDW files, use a free text editor to open it as a text document. Doing this might help you find some sort of information within the file itself that can explain the program that was used to create it, which can help you track down a compatible opener.

If you find that an application on your PC does try to open the file but it's the wrong application or you'd rather have another installed program open it, change which program opens MDW files by default.

How to Convert an MDW File

If your file was created in Access 2003, you can open it in a newer version through the command line. See this thread at Stack Overflow for specific instructions on opening an Access 2003 MDW file in Access 2010. Similar steps could be taken for a version newer than Access 2010.

For files that aren't associated with Access, the program that created it is most likely able to convert it to a new format. This is usually possible through an Export menu of some kind.

Still Can't Open the File?

Some files look like they're related because of how similar their file extensions are spelled. But this rarely means that they can open with the same software.

For example, this Access format has nothing to do with the MarinerWrite Document format that uses the MWD file extension. Even though their file extensions are similar, MWD files are used with Mariner Write, not Microsoft Access.

This is also the case with MD and MDA files.

Additional Reading on MDW Files

If you're securing an MDW file to prevent access to it, it's important to create a new file altogether instead of using the default one that comes with Microsoft Access. This is because the default file called System.mdw, stores the same default credentials for accessing the database, on any and all computers that use Microsoft Access, meaning it's not at all secure by default.

Therefore, you shouldn't use the file that Microsoft supplies with Access but instead create your own. You can build your own custom MDW file in MS Access through the Tools > Security > Workgroup Administrator menu.

It's also important to always keep a backup so that you can avoid having to re-create all the user/group accounts that existed in the file if you happen to lose it. Building the file from scratch is a delicate process that must be done perfectly or you won't be able to access the database with the WIF.