No. The authenticity of the Declaration of Conformity can only be ensured by the responsible party (the manufacturer or their authorised representative). The contact information of the responsible party is indicated on the DoC and you can use this information to contact them directly.
In most cases, the number on the Declaration of Conformity refers to the identification number of the Notified Body that performed the conformity assessment. You can use this number to search for the Notified Body on the NANDO website. On this site you can also find an up-to-date list of all Notified Bodies per country and/or Directive.