Password Dialog
When the Spreadsheet control loads a password encrypted document and the EncryptionOptions.Password property is not set or contains a wrong password, and the SpreadsheetControl.EncryptedFilePasswordRequest event is not handled, the end-user is prompted for the password with the following dialog box:
You can handle the SpreadsheetControl.EncryptedFilePasswordRequest event and set e.Handled to true to not display this dialog. In the event handler, specify the password using the EncryptedFilePasswordRequestEventArgs.Password property.