How do you open an SDF file (SQL Server Compact Edition)?

Download and install LINQPad, it works for SQL Server, MySQL, SQLite and also SDF (SQL CE 4.0).

Steps for open SDF Files:

1. Click Add Connection

2. Select Build data context automatically and Default (LINQ to SQL), then Next.

3. Under Provider choose SQL CE 4.0.

4. Under Database with Attach database file selected, choose Browse to select your .sdf file.

5. Click OK.

Try the sql server management studio (version 2008 or earlier) from Microsoft. Download it from here. Not sure about the license, but it seems to be free if you download the EXPRESS EDITION.

You might also be able to use later editions of SSMS. For 2016, you will need to install an extension.

If you have the option you can copy the sdf file to a different machine which you are allowed to pollute with additional software.

Update: comment from Nick Westgate in nice formatting

The steps are not all that intuitive:

1. Open SQL Server Management Studio, or if it's running select File -> Connect Object Explorer...
2. In the Connect to Server dialog change Server type to SQL Server Compact Edition
3. From the Database file dropdown select < Browse for more...>
4. Open your SDF file.

You can open SQL Compact 4.0 Databases from Visual Studio 2012 directly, by going to

1. View ->
2. Server Explorer ->
3. Data Connections ->
4. Add Connection...
5. Change... (Data Source:)
6. Microsoft SQL Server Compact 4.0
7. Browse...

and following the instructions there.

If you're okay with them being upgraded to 4.0, you can open older versions of SQL Compact Databases also - handy if you just want to have a look at some tables, etc for stuff like Windows Phone local database development.

(note I'm not sure if this requires a specific SKU of VS2012, if it helps I'm running Premium)