B2 visa to H1-B visa conversion

My H1-B Visa petition is valid till 30th Sep 2018 for New Jersey Parsippany location and further extendable to another 3 years.I don’t have H1-B stamped on my passport. I want to apply for B2 visitor visa from India .If I travel to US from India on B2 visa and then if any employer wants to convert my B2- visa to H1-B visa then is it possible ?I have already been to US for 2.3 years.I have US SSN number and Driving license also. Currently I am in India. When I reach there in US on B2 visitor visa and if I get any job offer and then employer is ready to transfer my H1-B visa then Is it possible to get approval from USCIS ?What are the risks ?