Am I allowed to pass on files to a graphic designer?

Yes! You may pass it on to a graphic designer doing work for you. The designer himself is, however, not allowed to use that file for other customers, including himself.

This is independent of the type of licence you have taken.

Look for section 6B of the current licencing agreement.

(B) Employee and Contractor Use. You may transfer files containing the Stock Assets, including productions, Projects, or other permitted derivative materials, to employees or subcontractors, provided that:
(1) such employees and subcontractors agree in an enforceable written agreement to abide by the restrictions in the Terms;
(2) such employees and subcontractors only use the Stock Assets on your behalf; and
(3) you are solely responsible and liable for use of the Stock Assets by your employee or contractor.

Look here for more information on licensing: https://community.adobe.com/t5/stock/links-for-licensing-terms/td-p/11366788
(Disclaimer: As always with licensing, this is my interpretation of the rules. I think they are correct and advice is based on reading and interpreting the licence terms and on fair use for both the buyer and the artist/stock company, but I cannot rule out that my interpretation is wrong. I'm not an Adobe employee).