No, work experience is not complusory for doing a regular MBA or PGDM, but yes, it definitely is an advantage. Many B Schools do give weightage and preference to candidates with work-ex. However if you want to pursue it immediately after your under graduation you may go ahead with it.

Executive MBA/PGDM is meant specifically for corporate executives and managers who continue to hold a job or take a break to enhance their qualification.

No work experience is not at all a compulsion to get admission in a Bschool. Each college offering MBA course (PGDM) has a set criteria of admitting students with and without work-ex.
Now, when I talk about freshers, I am particularly talking about those who are in the final year or just completed graduation while appearing for CAT (not those who have a gap, however, students with gap also don't have much problem as such, but they are a little disadvantaged as compared to other freshers)
As a matter of fact, every B- school right from IIMA, B, C have a minimum of 23% freshers, infact, IIM-Indore had a batch with 65% freshers.
Above all, you being a Fresher, your competition ultimately shall only be with the freshers, not with the students who have work experience.
So, relax, work hard and perform fiercely upon getting calls.
All the best!!