Hello Candidate,

MBA is a degree course offered by the colleges affiliated to the universities. So, only universities can offer MBA programmes.
PGDM is a diploma course offered by the institutes that are recognised by AICTE and which are autonomous and not affiliated to any university. However, accreditation by Association of Indian Universities (AIU) makes an institute's PGDM course equivalent to an MBA.
Note: It is not mandatory that a PGDM is equal to MBA because then the college offering the PGDM course must have accreditation from AIU
Good Luck!