Check the or app.config files of the original application. The connection string often contains the password in plain text or a reversible hash.
If the database was created as part of a development project, you might not need a "crack." sdf database password crack filel exclusive
If you have a vague idea of what the password might be (e.g., you know it was a specific length or used certain characters), you can write a simple C# script to automate login attempts. This is essentially a "legal" brute-force method that doesn't require downloading untrusted third-party binaries. Check the or app