Employee Bond is valid ? if it is only on Offer letter

I had joined an IT company in April'2015 with 2 Years and 5 Months of experience in the same domain/field. At the time of joining they signed me on the every pages of offer letter. Among the all clauses there is one like "Accepting this offer letter you are agreeing to work with Company Name at least One Year from the date of joining. Termination of employment in between will not be allowed or it will be considered based up on the situation or paying fine in lieu of pre termination. Else Company Name will have full authority to take a legal action against the employee for pre termination of his/her employment. However, Company Name has the full rights to end this contract and terminate your employment immediately for non-performance or any other situation." Moreover they took one of my original document. After 3-4 months I want to leave the organization immediately due to my health issue and family crisis. The probation period of the company is 6 months i.e. I am still not confirmed employee. They continuously threat me of the legal action if I will break the bond. Now Kindly you can tell me they can take any legal action on me or not. I've heard that the bond is always happened in some stamp paper with exact Amount and obviously both way, but in this case they had mentioned it only on Offer and Appointment Letters with taking the charge of the company only. Please help I need your help urgently. You can ask me any question related to this.