Conversion of pvt. ltd. company to public ltd.

Dear All,

I have a query regarding conversion of Pvt. Ltd. Company into Public Ltd. Company.

We want to convert a Pvt. Company to Public Company and that by giving it a retrospective effect from around 6-8 months back.

can it be done or not, or the status of public ltd. become operational from the date only after when it becomes Public company.

Can the effective date of conversion be 6-8 months back from actual date of conversion.

Regards

Ashwin