PGP or PGDM is a Post Graudate Program/Post Graduate diploma in Management offered by Instituitions approved by AICTE but not affiliated to any university, like IIMs. Now IIMs are converted into Institute of National Importance and can Award MBA degree.

MBA is  degree awarded by a University approved by UGC. Only Universities can offer Degree Programs and now Institute of National Importance (INI ) also.

PGDM is not equal to MBA but PGDM from Good instituition like IIMs are equally good in studies and job.

I shall help you with the basic difference.
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!