They cannot force you to buy but they may try to force you to move out. You do have certain rights as a tenant and they cannot simply throw you out on the street. Being that you do not have the ability to purchase the apartment they may ask you to leave. If you have a lease they will have to wait until your lease is up before they request for you to vacate. If you do not have a lease they may be sending you a 30 day notice shortly. Until that happens I would not panic. If it is impossible for you to get out within that 30 days after you recieve the letter, they will be able to start an eviction preceeding at that point in time and the case would be taken to court. This starts a process that can take 30 days to a year or more depending on the circumstances. I must also point out that I am not sure how this being an HDFC would effect what I am telling you. If you can afford it you may want to speak to a landlord tenant attorney (look for one on Google by doing a search for "landlord tenant attorney brooklyn"). Most attorneys will give you some information over the phone for free even if you do not hire them, so try to get in touch with one either way.
I have seen times where given the circumstances the landlord would compensate the tenant for leaving in a timely fashion ( like paying moving expenses, etc.), thus both parties would benefit, so keep that in mind. I hope it works out as best as it can for you, good luck.
Madison Estates & Properties, Inc.
Office: (718) 645-1665