Use Custom Software Development Rather Than Readymade Software
It is a complex process to convert developed software in a custom manner. Client should first explain his needs and requirement to the organisation which is going to design the software. The needs should be discussed in detail with the organisation. A contract should be signed between the organisation and the client and contract should include all the details regarding the custom software development such as time for production, cost, functionality etc.
Check whether the software will be made as a fresh one or will be re-modified one. If it is rebuilt then, there is another issue that should be discussed. Decide the type of security that the software is needed and make sure with the developing organisation that what type of security they will provide for the software. Apart from these clarifications, make technical aspects like the programming language used and other such things clear.