C# how to get text value from PasswordBox?

You can get it from the Password property.

You may extract it from Password property:

passwordBox.Password.ToString()

You may not want to store the password in clear text in memory, from the msdn doc you should use SecurePassword in order to prevent that.

Example: SecureString myPass = passwordBox.SecurePassword

https://docs.microsoft.com/en-us/dotnet/api/system.windows.controls.passwordbox.securepassword

If using a MaskedTextbox you can use the .text property. For example:

private void btnOk_Click(object sender, EventArgs e)
{
    if ( myMaskedTextbox.Text.Equals(PASSWORD) )
    {
        //do something
    }         

}