"data source master key " forgotten password

There nothing we can do because it used for the encryption of the Xml. However we had a bug in a old version where sometime the masterkey saved was ********

You could give it a try

Where the file! I have not found! Is the document, or is the registration form inside?

It's usually connections.xml located in %LocalAppData%\Devolutions\RemoteDesktopManager and the file is encrypted with the masterkey