A 6D doesn't address payments to individuals, it addresses payments to a condo association. A 6D establishes limits on back dues and assessments and it would be very unwise to transact without one.
It sounds like you're the purchaser. Trust me when I say this: Get an attorney to help you, and have the attorney review the situation. Attempting to buy a post foreclosure condo without help, is a bad idea.
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Your statement that nothing has been paid in the past to the other owner troubles me as you can not do this on your own. Either there is an obligation or not as described in the condo documents . Past practice is no guide- if the other owner paid bills because he did not want to spend the time needed to deal with a large inefficent bank does not mean you get a free ride. I think you need an attorney
A 6d certificate is necessary to show what the status of the outstanding condo fees are against a particular unit. As a buyer moving forward without obtaining a "clean" 6d certificate you are potentially opening yourself up to unnecessary liability. You should consult a lawyer before moving forward.