A partnership agreement is not mandatory but strongly recommended by the EC and REA. According to the Guide for Applicants (RISE 2015, p. 11): 'Financial aspects between partner organisations and beneficiaries are dealt within the partnership preferably by means of a Partnership agreement." The Work Programme 2014-15 states on p. 39 "Consortia involving partner organisations are encouraged to sign a partnership agreement to regulate the relationship between participants. These partnership agreements shall be in compliance with the obligations laid down in the Agreement."
It should be signed by the authorized representatives of the institution, as it concerns the financial aspects, otherwise such a partnership would not have a legal power.