The 26-year-old played 90 minutes as a trialist at right-back for the Dons' U20s as they beat Hibs 1-0 in the Development League in February.
Adejo, who can also play in central defence, was with AEL Kalloni in Greece last season.
He had previously played in Italy for Reggina from 2008 to 2014.
Source: Sky Sports